please help about ratio and proportion

Q1- A Contractor agree to lay a road 3000m long in 30 days. He employs 50 men who work for 8 hours a day. After 20 working days, he finds that only 1200m of the road is completed. How many more men should he employ to finish the work on time if each man now works 10 hours a day?

Q2- To paint a house john takes 6 days, peter takes 4 days and Paul takes 12 days. How many days will they take if they work together?

Q3- Three pipes fill a swimming pool in half an hour. If two of them take 1.5 hours and 1.3333 hours respectively to fill it alone. How many hours will the third pipe take to fill it alone?