Answer
$4|b|$
Work Step by Step
Using $\sqrt{x^2}=|x|$, the given expression, $
\sqrt{(-4b)^2}
,$ simplifies to
\begin{array}{l}
|-4b|
\\\\=
4|b|
.\end{array}
Note: We have to put the variable in absolute value bars since it is being raised to an odd power.