$A$ and $B$ can do a piece of work in $18$ days,$B$ and $C$ in $24$ days,and $A$ and $C$ in $36$ days. In what time can they do it all working together? (in days)

$5$ men and $5$ women earn $Rs. 660$ in $3$ days. $10$ men and $20$ women earn $Rs. 3500$ in $5$ days. In how many days can $6$ men and $4$ women earn $Rs. 1060$?

$A$ can complete a work in $10$ days,$B$ in $12$ days,and $C$ in $15$ days. All of them began the work together; but $A$ had to leave the work after $2$ days of the start and $B$ also left $3$ days before the completion of the work. How long did the work last? (in days)

Four examiners can examine a certain number of answer papers in $10$ days by working for $5$ hours a day. For how many hours in a day would $2$ examiners have to work in order to examine twice the number of answer papers in $20$ days?

$A$ and $B$ together can complete a work in $3$ days. They start together,but after $2$ days,$B$ left the work. If the work is completed after two more days,in how many days would $B$ alone do the work?

One man,$3$ women,and $4$ boys can do a work in $96$ hours,$2$ men and $8$ boys can do it in $80$ hours,and $2$ men and $3$ women can do it in $120$ hours. In how many hours can it be done by $5$ men and $12$ boys? (in hours)