A goal for many elite runners is to complete a mile in 4 minutes. At what speed (in miles per hour)

A goal for many elite runners is to complete a mile in 4 minutes. At what speed (in miles per hour) is a runner traveling when he completes a mile in 4 minutes?

4 minutes/60 minutes per hour = 1 mile / n miles

4/60 = 1/15, so n = 15 miles per hour