There's 3600 seconds in 1 hour. 3600 seconds divided by 70 miles per hour is 51 and 1/2 seconds to go 1 mile. ANSWER: Exactly 51.428571428571428571428571 seconds to go 1 mile at 70 miles per hour.

To get how long it takes to go any speed over 1 mile use this formula. With X being your desired speed. (60/X) times 60