One of the challenges in the last mission is to kill the HVTs in the farm area within 3 seconds. What's that mean? I thought that it meant to kill the first two people within three seconds of each other, but I'm pretty sure I did that with my sync shot, and it didn't say I did the challenge. Were those the wrong guys, or is that not what it means by three seconds?
It's the middle three people, but you are right on how on how to kill them:
Also watch this video on how to do it.