Function $f$ is a quadratic function where $f(-20)=0$ and $f(-4)=0.$ …

Question

Prompt

Function

f

is a quadratic function where

f (- 20) = 0

and

f (- 4) = 0.

The graph of

y = f (x)

has a vertex at

(r, - 64) .

What is the value of

r