Answer
Approximately $11.02mi/h$
Work Step by Step
Let the terminal velocity be $V$
Parachutist's weight $w$
And the constant of proportionality $k$
According to the information given, we can write the following equation:
$V=k\sqrt{w}$
$w=160lb$
$V=9mi/h$
$k$ is unknown
$9=k\sqrt{160}$
$k=\frac{9}{4\sqrt{10}}$
If $w=240lb$
$V=\frac{9}{4\sqrt{10}}\times \sqrt{240}=\frac{9\times4\sqrt{15}}{4\sqrt{10}}=\frac{9\sqrt{15}}{\sqrt{10}} = \frac{9\sqrt{15}\times\sqrt{10}}{\sqrt{10}\times\sqrt{10}}=\frac{5\times9\sqrt{6}}{10}=4.5\sqrt{6}\approx11.02mi/h$
