Explanation:
1 mile = 5280 ft
1 hour = 3600 seconds
65 miles / hour =
= 65 × 5280 ft / 3600 seconds = 65 × 528 ft / 360 s =
= 13 × 264 ft / 36 s = 13 × 66 ft / 9 s = 13 × 22 ft / 3 s =
= 13 × 11 ft / 1.5 s = 143 ft / 1.5 s
so, at 65 mph the driver travels 143 ft before the driver reacts (1.5 s) to an obstacle.