#### Answer

The student must cancel out common factors in all terms, not just in some of them.

#### Work Step by Step

In order to simplify these expressions, we look for common factors in the numerator and the denominator. This means that we need to be sure that the numerator and denominator are in fully factored form. Doing this, we find:
$$\frac{\left(x+4\right)\left(x+12\right)}{\left(x+4\right)^2}\\ \frac{x+12}{x+4}$$