If P and Q work together, they will complete a job in $7.5$ days. However, if P works alone and completes half the job and then Q takes over and completes the remaining half alone, they will be able to complete the job in $20$ days. How long will Q alone take to do the job if P is more efficient than Q?

G is twice as fast as S in doing work. If G can do a work in $30$ days less than S, how many days will they take to complete the work together? 

1.$25$
2. $20$
3. $22$
4.$15$ 

Ten people can do a work in $30$ days. In how many days, can 15 people complete double the work - 

1.$40$

2. $25$

3. $20$

4. $45$ 

A and B working alone can do a work in $20$ days and $15$ days respectively. They started the work together but B left after sometime and A finished the remaining work in $6$ days. Find after how many days from start B left the work?