17. In his motorboat Marvin can go downstream in 2 hours less time than he can go upstream the same distance. If the current is 5 mph, how fast can Marvin travel in still water if it takes 5 hours to travel upstream the given distance?

18. A cheetah can run 20 mph faster than a lion. A cheetah can run 3 miles in the same time that lion can run 2 miles. Find the speed of each animal.

19. A canoeist paddled for 5 hours down the river (with the current) to reach a campsite. The return trip against the same current took 7.5 hours. If the speed of the canoe in still water is 15 km/h, nd the speed of the current.