Answer
$25$ skateboards
Work Step by Step
Equating the cost expression, $C=100+20x$, and the revenue expression, $24x,$ then the number of skateboards, $x$, to break even is
\begin{array}{l}\require{cancel}
100+20x=24x
\\\\
100=24x-20x
\\\\
100=4x
\\\\
\dfrac{100}{4}=x
\\\\
x=25
.\end{array}
Hence, $\text{
$25$ skateboards
}.$
