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?