Kevin,

It depends on the units you want to use. If you want your speed in miles per minute then it's 3/28 = 0.107 miles per minute.

Suppose you want the speed in feet per second. There are 5280 feet in a mile so 3 miles is 3 × 5280 feet. There are 60 seconds in a minute so 28 minutes is 28 × 60 seconds. Thus 3 miles in 28 minutes is 3 × 5280 feet in 28 × 60 seconds or

(3 × 5280)/(28 × 60) = 15840/1680 = 9.43 feet per second.

Penny