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You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

EDIT: At the request of @aytimothy here is an explanation of an item sorter. An item sorter is a device which uses hoppers to sort through items.
They take items and extract a certain type of item and send it to an output hopper(or chest or whatever you want to use). An example of a schematic of an item sorter:

The 'I' and 'O' in the image is the 'Input Hopper' and 'Output hopper' respectively

You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

You need to make the following system

1. First take the input from the input hopper and pass it through an item sorter, to check which paper is passed through
2. Then you need to take your input from the item sorter, and since you know which one it is, dump it into an appropriate chest
3. Take a comparator output from the chest, and use it to display whatever output you want to be shown.

An example of what i am saying
The person wants to get into room A, and puts in the key of that room into the input hopper. This gets passed through an item sorter which checks that the key labelled 'A' has been passed through. Then the key is put from the item sorter into a chest. A comparator takes an output from the chest and opens up the door to room A. Then the key is taken and given to the person once he goes into room A.

EDIT: At the request of @aytimothy here is an explanation of an item sorter. An item sorter is a device which uses hoppers to sort through items.
They take items and extract a certain type of item and send it to an output hopper(or chest or whatever you want to use). An example of a schematic of an item sorter:

The 'I' and 'O' in the image is the 'Input Hopper' and 'Output hopper' respectively