(9b -7) +(7-3b) - (-3-3b) +(6+3b) = 9b -7 + 7-3b +3 + 3b + 6+3b = 12b + 9
We have 4 numbers (9b -7) and (7-3b), and - (-3-3b), and (6+3b).
To find the average, we need the sum of these numbers 12b + 9, divide by 4.
(12b + 9)/4 = 3b +9/4
Answer is A.
