1. Factor out common terms in the first two terms, then in the last two terms:
x^2(x + 4) - 9(x + 4)
2. Factor out the common term x + 4
(x + 4)(x^2 - 9)
3. Rewrite x^2 - 9 in the form a^2 - b^2, where a = x and b = 3
(x + 4)(x^2 - 3^2)
4. Use Difference of Squares: a^2 - b^2 = (a + b)(a - b)
(x + 4)(x + 3)(x - 3)