Answer
$\color{blue}{(a+b+4)(a+b-4))}$
Work Step by Step
Note that $16=4^2$.
Thus, the binomial above is equivalent to:
$=(a+b)^2-4^2$
Factor the binomial using the formula $x^2-y^2=(x+y)(x-y)$ where $x=a+b$ and $y=4$ to obtain:
$=[(a+b)+4][(a+b)-4]
\\=\color{blue}{(a+b+4)(a+b-4))}$
