AAMC CBT 11 question 31

Hi,
I had a question with regards to this problem as I don't quite see why we can't assign g as being -10m/s^2? The Wg is going down and the Air resistance is going up Wa, so why isn't Wa positive? Also, could someone help me with finding the work done by Air Resistance, should it not be the same?

Thanks in advance!