16. If 18 pumps can raise 2170 tonnes of water in 10 days, working 7 hours a day, in how many days will 16 pumps raise 1736 tonnes, working 9 hours a day ?

17. If 5 men working 6 hours a day can reap 3 field in 20 days, in how many days will 15 men reap the field, working 8 hours a day ?

18. 20 men complete one-third of a piece of work in 20 days. How many more men should be employed to finish the rest of the work in 25 more days ?