(+8)+(-9)
the answer is -1
Solution:
Given the mean and standard deviation;

The z-score formula is;

(a)

(b)

(c)
C=15+X
C being the total cost. Starting at $15 plus an additional $1 (seen as X in the equation) for each student.
Answer:
5.25 + 5.25 = 10.5
8.5 - 3.25 = 5.25
so
5.25 & 8.5 are the answers consequently