The formula d = rt gives the distance traveled in time t at rate r.

If a bicyclist rides for 2.3 hours and travels 41 miles, what was her average speed?
A. 9.43 miles per hour B. 5.6 miles per hour C. 17.83 miles per hour D. 38.7 miles per hour

The answer would be D. 38.7 miles per hour.
To figure this out you must replace the d with 41 and the t with 2.3 so you get an equation that looks like this, 41=r-2.3.
With this you can easily subtract 41-2.3 and you get 38.7 as the r.