Answer
$12 \text{ hours }$
Work Step by Step
Let $x$ be the time for Steve to word process the paper alone. Expressed in $1$ unit/part, the rates are related as
\begin{array}{l}\require{cancel}
\dfrac{1}{6}+\dfrac{1}{x}=\dfrac{1}{4}
.\end{array}
Using the $LCD=
12x
,$ and the properties of equality, then
\begin{array}{l}\require{cancel}
12x\left(\dfrac{1}{6}+\dfrac{1}{x}\right)=\left(\dfrac{1}{4}\right)12x
\\\\
2x+12=3x
\\\\
12=3x-2x
\\\\
12=x
.\end{array}
Hence, it takes $
12 \text{ hours }
$ for Steve to word process the paper alone.
