Meg rowed her boat upstream a distance of 91 miles and then rowed back to the starting point. The total time of the trip was 20 hours. If the rate of the current was 3 mph, find the average speed of the boat relative to the water.

Solution:

The speed of boat is x

91/(x+3)+91/(x-3)=20

x=10

So the speed of boat is 10 mph