The circumference of the tire would be: 28 x PI = 87.96 inches = 88 inches.
88 inches / 12 inches = 7.33 feet
Every revolution the tire would travel 7.33 feet.
1 mile = 5,280 feet
3 miles = 5280 x 3 = 15,840 feet total.
Divide total feet by the circumference of the tire:
15,840 / 7.33 = 2,161 revolutions.