Use the fact that for a power function $y=k x^{n},$ for small changes, the percent change in output $y$ is approximately $n$ times the percent change in input $x$. (See Problem 88.)
The stopping distance $s,$ in feet, of a car traveling $v$ mph is $s=v^{2} / 20 .$ An increase of $10 \%$ in the speed of the car leads to what percent increase in the stopping distance?