$15$ 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 do a certain work in $12$ days. $B$ is $60\%$ more efficient than $A$. How many days will $B$ and $A$ together take to do the same job?

If $6$ men and $8$ boys can do a piece of work in $10$ days and $26$ men and $48$ boys can do the same work in $2$ days,the time taken by $15$ men and $20$ boys to do the same type of work will be (in days)

$A$ and $B$ together can do a piece of work in $30$ days. $A$ having worked for $16$ days,$B$ finishes the remaining work alone in $44$ days. In how many days shall $B$ finish the whole work alone?

$A$ can finish a work in $18$ days and $B$ can do the same work in $15$ days. $B$ worked for $10$ days and left the job. In how many days can $A$ alone finish the remaining work?

$10$ men working $6\, \text{h}$ a day can complete a work in $18\, \text{days}$. How many $\text{hours per day}$ must $15$ men work to complete the same work in $12\, \text{days}$?