Rather Frustrating

So, today in class we were given eight pairs of math problems. Out of each pair, we had to select the more difficult problem. Okay. Fine. That wasn't so bad. The following activity was (and is) rather difficult. We were given 11 problems, all similar content. It's frustrating. I don't know what criteria to judge these problems off of. I'm hoping to talk with some friends who can help me out. Addition, subtraction, etc. are not acceptable criteria. I'm frustrated.