A motorboat travels 9 miles downstream (with the current) in 30 minutes. The return trip upstream (against the current) takes 90 minutes. Which system of equations can be used to find x, the speed of the boat in miles per hour, and y, the speed of the current in miles per hour? recall the formula d = rt. 9 = 0. 5(x – y) 9 = 1. 5(x + y) 9 = 1. 5(x – y) 9 = 0. 5(x + y) 0. 5 = 9(x – y) 1. 5 = 9(x + y) 1. 5 = 9(x – y) 0. 5 = 9(x + y).