Appendix A - Review - A.3 Polynomials - A.3 Assess Your Understanding - Page A29: 13

$(d)$

First, factor out the CGF, which is $4$: $4x^{2}-8x-60=4(x^{2}-2x-15)$ Now, when factoring $x^{2}+bx+c$, we search for two factors of $c$ whose sum is $b$. Two factors of $c=-15$ whose sum is $-2$ are $-5$ and $3$. Thus, the factored form of $x^2-2x-15$ is $(x-5)(x+3)$. Therefore, the completely factored form of the given polynomial is: $$4(x-5)(x+3)$$