You have the following polynomial:
5x² + 30x + 45
in order to factorize the previous expression, multiply and divide by 5:
(5x² + 30x + 45)(5/5) =
(x² + 6x + 9)(5)
next, consider that the first factor is a perfect square, in fact:
x² + 6x + 9 = (x + 3)² = (x + 3)(x + 3)
then, you have:
(x² + 6x + 9)(5) = (x + 3)(x + 3)(5)
finally, enter 5 factor into one of the algebraic factors:
(x + 3)(x + 3)(5) = (5x + 15)(x + 3)