The highway patrol uses the following formula to estimate the speed (s), in miles per...

The highway patrol uses the following formula to estimate the speed (s), in miles per hour, at which a car was traveling if the car skidded d feet before stopping after the brakes were applied:

The variable f relates to the friction of the road surface. The following table estimates ffor certain types of road surfaces and conditions.

If a car skids 80 feet on wet gravel, what is the approximate speed, in miles per hour, at which the car was traveling?