22. 2 men and 7 boys can do piece of work in 14 days; 3 men and 8 boys can do the same in 11 days. 8 men and 6 boys can do 3 times the amount of this work in :

23. If 5 engines consume 6 metric tones of coal when each is running 9 hours day, how much coal will be needed for 8 engines, each running 10 hours a day, it being given that 3 engines of the former type consume as much as 4 engines of latter type ?

24. If 20 men can build a wall 112 metres long in 6 days, what length of a similar wall can be built by 25 men in 3 days ?