Answer
$2 \text{ hours}$
Work Step by Step
Let $x$ be the time it takes to finish the job when both work together.
In terms of $1$ part/unit, the rates are related as
\begin{array}{l}\require{cancel}
\dfrac{1}{3}+\dfrac{1}{6}=\dfrac{1}{x}
.\end{array}
Using the $LCD=6x$ and the properties of equality, the equation above is equivalent to
\begin{array}{l}\require{cancel}
6x\left(\dfrac{1}{3}+\dfrac{1}{6}\right)=\left(\dfrac{1}{x}\right)6x
\\\\
2x(1)+x(1)=6(1)
\\\\
2x+x=6
\\\\
3x=6
\\\\
x=\dfrac{6}{3}
\\\\
x=2
.\end{array}
Hence, the time it takes to finish the job when both work together, $x,$ is $
2 \text{ hours}
.$
