Please help me find the answer

Question

f(x) = (x − 5)(x − 8)(x − 9),    [5, 9]

find all values of c in the open interval (a, b) such that f '(c) = 0 (Enter your answers as a comma-separated list)

C=

Answer 1

Expand f(x)

Determine f'(x)

Set f'(x) = 0.

Solve for x.