Let x be the boat speed in still water (in miles per hoyr). Let y be the speed of the current. Then from the condition x + y = 24/2 = 12, (1) x - y = 24/4 = 6 (2) To solve the system, add the equations. You will get 2x = 12 + 6 = 18 ====> x = 18/2 = 9. Answer. The boat speed in still water is 9 mph.