Directions: Answer the questions independently of each other. X can do a piece of work in 20 days working 7 hours a day. The work is started by X and on the second day, one man whose capacity to do the work is twice that of X, joined in. On the third day, another man whose capacity is thrice that of X, joined in and this process continued till the work was completed. In how many days will the work be completed, if everyone works for four hours a day?