Let u be the rate of the boat in the first 5 hours. Then the rate of the boat is (u-4) in the last 3 hours. Your equation for u is the "distance" equation 5u + 3(u-4) = 132. 8u - 12 = 132 ---> 8u = 132 + 12 ---> 8u = 144 ---> u == 18. The speed of the boat during first 5 hours was 18 miles per hour. Hence, it covered the distance of 5*18 = 90 miles during the first 5 hours.