[tex] \frac{20 ft}{sec} ( \frac{60 sec}{min} )( \frac{60 min}{hr})( \frac{1 mi}{5280 ft}) [/tex]
All of the units cancel other than miles divided by hours which is what we need.
Now we do (20 * 60 * 60 * 1) / 5280 which is 13.636363 (repeating) or 13.6364 miles per hour.
