Hi!
To find the average of any group of numbers all you need to do is add all the numbers together and then divide by the amount of numbers there are in the group. e.g. 1, 2, 3 add to get 6 then divide by three to get 2 as an average.
^ ^ ^
there are three numbers so divide by 3
So the answers to A. and B. are:
A. 5
B. -4