From the condition, you have these 3 equations A + B + C = 3700 (1) A + B = 2200 (2) A + C = 2400 (3) To find C, from equation (1) subtract equation (2) : C = 3700-2200 = 1500 gallons per hour. To find B, from equation (1) subtract equation (3) : B = 3700-2400 = 1300 gallons per hour. To find A, substitute the value of B= 1300 into equation (2) A + 1300 = 2200, which gives you A = 2200 - 1300 = 900 gallons per hour.