#### Answer

$(x+7)(x-4)$

#### Work Step by Step

Regroup the terms to obtain:
$=(x^2+7x)+(-4x-28)$
Factor out the greatest common factor of each group to obtain:
$=x(x+7) + (-4)(x+7)$
The $GCF$ for the two terms is a binomial, $(x+7)$. Even though it is a binomial, we can factor it out just like we would factor out a number or a variable. Thus, we factor out the binomial to obtain:
$=(x+7)[x+(-4)]
\\=(x+7)(x-4)$