$A$ job can be completed by $12$ men in $12$ days. How many extra days will be needed to complete the job if $6$ men leave after working for $6$ days?

$P$ and $Q$ complete a certain work in $30 \, days$,$Q$ and $R$ in $40 \, days$,while $R$ and $P$ in $60 \, days$. How long will they take to finish it together? (in $days$)

$A$ farmer can plough a field working $6$ hours per day in $18$ days. How many hours per day must the farmer work to finish the same work in $12$ days?

$12$ men complete a work in $9$ days. After they have worked for $6$ days,$6$ more men join them. How many days will they take to complete the remaining work?

$A$ can do a piece of work in $8$ days. $A$ undertook it for $Rs. 320$. With the help of $B$,he finishes the work in $6$ days. $B$'s share is (in $Rs.$):

$A$ and $B,$ working separately,can complete a piece of work in $9$ and $12$ days,respectively. If they work for a day alternately,$A$ beginning,in how many days will the work be completed?