#### Answer

$s=5.33$ mi/h

#### Work Step by Step

Since $F$ varies jointly with $A$ and the square of $s$, we have:
$F=kAs^{2}$
We are given: $F=220$ and $A=40$ and $s=5$, so we have:
$220=k*40*5^2$
$220=1000k$
$k=220/1000=0.22$
Therefore:
$F=0.22As^2$
Now we plug in $A=28$ and $F=175$ to find $s$:
$175=0.220*28*s^{2}$
$175=6.16s^2$
$28.409=s^{2}$
$s=\sqrt{28.4090}=5.33$ mi/h