A is twice as good a workman as B and together they finish a piece of work in 14 days. The number of days taken by A alone to finish the work, is

A and B are two taps which can fill a tank in 10 minutes and 20 minutes. However, there is a leakage at the bottom which empty a filled tank in 40 minutes. If the tank is empty initially, how much time will both the taps take to fill the tank?

16 men can complete a work in 35 days. In many days can 28 men complete the same piece of work?