$15$ men take $20$ days to complete a job working $8$ hours a day. The number of hours a day $20$ men should work to complete the same job in $12$ days is:

$A$ can finish a work in $18$ days and $B$ can do the same work in half the time taken by $A$. Then,working together,what part of the same work can they finish in a day?

$A$ work can be completed by $P$ and $Q$ in $12$ days,$Q$ and $R$ in $15$ days,and $R$ and $P$ in $20$ days. In how many days can $P$ alone finish the work?

$6$ men or $12$ women can do a piece of work in $20$ days. In how many days can $8$ men and $16$ women do twice as big as this work?

$A$ can do a piece of work in $14$ days,which $B$ can do in $21$ days. They begin together,but $3$ days before the completion of the work,$A$ leaves. The total number of days to complete the work is:

Ajay and Sunil together can complete a piece of work in $10$ days,Sunil and Sanjay in $15$ days,and Sanjay and Ajay in $20$ days. They worked together for $6$ days,and then Ajay leaves. Sunil and Sanjay worked together for $4$ more days,and Sunil leaves. How long will Sanjay take to complete the remaining work? (in days)