Answer:
(y - 3)^4
Explanation:
The greatest common factor does not include either the 2 or the 5. Both of these numbers are prime; they have nothing in common.
But the binomials do have something in common.
You could write them like this to see what I am about to tell you.
(y - 3)^4 = (y - 3)*(y - 3)*(y - 3)*(y - 3)
(y - 3)^5 = (y - 3)*(y - 3)*(y - 3)*(y - 3)*(y - 3)
The common factor in both of these is (y - 3)^4 which is in bold results.