The GCF of 90 and 27 is 9.
Divide both numbers by the GCF: 90/9 = 10 and 27/9 = 3
9 is going to be the number you multiply outside the parenthesis. (10 + 3) is going to be inside the parenthesis.
9(10 + 3)
We can check by using the distributive property; a(b + c) = ab + ac
(9 * 10) + (9 * 3) = 90 + 27
Best of Luck!