[tex]\bf \textit{pythagorean theorem}\\\\
c^2=a^2+b^2\implies c=\sqrt{a^2+b^2}\qquad
\begin{cases}
a=20\\
b=13.5
\end{cases}
\\\\\\
c=\sqrt{20^2+13.5^2}\implies c=\sqrt{582.25}\implies c\approx 24.12985702402730
\\\\\\
c\approx 24.1\impliedby \textit{rounded up}[/tex]