Question #1. The correct philosophy for the PMP exam is to eliminate two wrong or weak answers and determine the best (or least worst) answer from the remaining two (which on the exam is harder than you think).
Let's see if we can find some weaker answers. Let's think about #1: why would discussing this missed requirement need customer approval? I mean they approved the requirement already. So #1 is off the list. #4 seems weak because we don't need a change request to do the work we were supposed to do in the first place! I'd nix #4. Now we are down to #2 and #3.
Let's think logically about these two. Which would I do first? Since I know it's one person for one week, I could run off and look at the schedule and cost. But does that sound reasonable? What about #3? What if I do that first, perhaps it would take two people 2.5 days, or 3 people 1.6 days? You see once I KNOW that I'm efficiently applying resources to get the job done quickly could I then double-check the triple constraint.
Thus #3 becomes the best option. And when you get here, you should feel like you've been on a little story journey. Does this make sense in the context of the answer? Yes, I know that all the other paths feel wrong and I'm on solid ground. Final answer.
Hope this helps.