Answer
The first step is wrong.
Work Step by Step
The error is in the first step. The student should replace the division sign with the multiplication sign.
The correct steps are shown below.
$=\frac{3a}{a+2}\div \frac{(a+2)^2}{a-4}$
$=\frac{3a}{a+2}\times \frac{a-4}{(a+2)^2}$
Multiply the fractions.
$=\frac{3a(a-4)}{(a+2)^3}$
