F(x) in math

Question: What is the average rate of change of f(x) = 5x + 4 over [5, 6] ?(f x math)

A ) - 12500
B ) 3129
C ) 15629
D ) 12500

Steps to derive

1 Here f(x) = 5x + 4, x changes from a = 5 to b = 6.

2 The average rate of change of f(x) = f(b) - f(a)b - a
[Definition.]

3 = f(6) - f(5)6 - 5

4 = 15629 - 31291
[Simplify.]

5 = 12500