An inverse variation is defined as
[tex]y=\frac{k}{x}[/tex]Where x = 80 and y = 60, let's find k
[tex]\begin{gathered} 60=\frac{k}{80} \\ k=60\cdot80=4800 \end{gathered}[/tex]Then, we use the constant k to find x when y = -20.
[tex]\begin{gathered} y=\frac{4800}{x} \\ x=\frac{4800}{y}=\frac{4800}{-20} \\ x=-240 \end{gathered}[/tex]