Use the formula d = rt (where d is the total distance traveled, r is the average rate of travel, and t is the total time taken to travel the distance given) to solve this problem.
We'll simply substitute the known values in and solve for r.
3 = 0.75r (The reason I am substituting 0.75 for t instead of 45 is that the problem is asking for how fast he travels in terms of miles per HOUR, not hours per minute. 45 minutes is 0.75 of 1 hour.)
4 = r
Barry walked at an average speed of 4 miles per hour!
