Answer
$(3a)b$
Work Step by Step
$\bf{\text{Solution Outline:}}$
Regroup the product of the terms in the given expression, $
3(ab)
.$
$\bf{\text{Solution Details:}}$
The Associative Law of Multiplication states that $a(bc)$ is the same as the $(ab)c.$ Hence, the given expression is equivalent to
\begin{array}{l}\require{cancel}
(3a)b
.\end{array}