Hi there!
There are 5,280 ft in a mile so multiply that by 60
5,280 × 60 = 316,800 ft
There are 60 min in an hour and 60 sec in a minute so multiply 60 sec by 60 sec
60 sec × 60 min = 3600 sec
Now divide 316,800 ft by 3600 sec to get:
316,800 ft ÷ 3600 sec ≈ 88 (ft/s)