The average of a group of numbers can be found by dividing their sum by the size of the group. In this case, each problem involves two numbers, so the pair would be added and then halved.
a. 3 + 43 = 46
46 / 2 = 23
b. (-7.5) + 7.5 = 0
0 / 2 = 0
c. (-8) + 7 = (-1)
(-1) / 2 = (-1/2)