Step-by-step explanation:
14/2 =7 so
(x+7)^2 + [ ]
if you were to multiply just the (x+7)^2 term it would look like x^2 +14x+49, but we need that final term to be equal to 64, so you can add 15 on to the end to make up for the gap.
This should get you
f(x) = (x+7)^2 + 15
