$f(x)=(x-a)(x-b)$ The function $f$ is defined by the given equation, …

Question

Prompt

f (x) = (x - a) (x - b)

The function

f

is defined by the given equation, where

a

and

b

are integer constants. If

f (15) > 0

f (18) < 0

, and

f (21) > 0

, what is one possible value of

a + b