Given the formula:

D=[tex]\frac{v^2}{64.4(F+G)}[/tex]

where:

D = breaking distance in feet

v = speed of car (feet per second) when breaks are applied

F = coefficient of friction (no units, number between 0 and 1)

G = grade of the road (no units expressed as decimal)

A car takes 63 feet to complete to a stop after its driver applies the brakes. The grade of the road is 0.01 and the coefficient of friction is 0.5. How fast was the car moving, in miles per hour, when the brakes were applied?

How would the answer be 31 miles an hour? I've tried endless combinations of numbers but I keep getting the wrong answer and I don't know if there's some hidden formula for this that I am missing as well to be able to solve the problem correctly...