$39$ persons can repair a road in $12$ days working $5$ hours per day. In how many days will $30$ persons working $6$ hours per day complete the same work?

$P$ 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 $days$)

$A$ 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)

$A$ labourer can do a job in $36 \text{ hours}$. After $9 \text{ hours}$,he takes a break. What fraction of the job is yet to be done?

$A$ 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 $A$ can complete a work in $16$ days,then in how many days can he complete $\frac{3}{4}$ of the work?