keeping in mind that there are 60 minutes in 1 hour, thus 240 kilometers per hour is just 240 kilometers in 60 minutes.
[tex] \bf \begin{array}{ccll}
minutes&km s\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
60&240\\
20&x
\end{array}\implies \cfrac{60}{20}=\cfrac{240}{x}\implies 3=\cfrac{240}{x}
\\\\\\
x=\cfrac{240}{3}\implies x=80 [/tex]
