Remark
The average is going to be (x + y + z)/3
Givens
x = (m + 9) / 2
y = (2m + 15) / 2
z = (3m + 18) / 2
Formula
average = (x + y + z)/3
Total = ((m + 9)/2 + (2m+15)/2 + (3m + 18)/2 ))
Solution
Total = (m + 2m + 3m) / 2 + (9 + 15 + 18) / 2
Total = ((6m + 42) / 2 )
Total = 6m/2 + 42/2
Total = 3m + 21
Average = (3m + 21)/3
Average = 3m/3 + 21/3
Average = m + 7
Answer = B
