How to approach this problem. I tried to make a eq like x^2 - 8x + 15, but it does not lead me anywhere. Any other ideas?

LINK https://new.gregmat.com/problems/problem/the-function-has-two-real-roots

How to approach this problem. I tried to make a eq like x^2 - 8x + 15, but it does not lead me anywhere. Any other ideas?

LINK https://new.gregmat.com/problems/problem/the-function-has-two-real-roots

A function got f(x) = 3 , 5 as one of the solutions

Now they ask possible solution for f(x+2).

(x+2) = 3 ---->Eq1

(x+2) = 5 ---->Eq2

From Eq 1 and 2, possible solutions are

x = 1 , 3