$A$ and $B$ can together complete a task in $18$ hours. After $6$ hours, $A$ leaves. $B$ takes $36$ hours to finish the rest of the task. How many hours would $A$ have taken to do the task if he worked alone?

Working efficiencies of $A$ and $B$ for completing a piece of work are in the ratio $3: 4$. The number of days taken by them to complete the work will be in the ratio:

$4$ men and $6$ women earn $Rs. \, 1600$ by doing a piece of work in $5$ days. $3$ men and $7$ women earn $Rs. \, 1740$ by doing the same work in $6$ days. In how many days can $7$ men and $6$ women complete the same work while earning $Rs. \, 3760$?

$A$ contractor undertakes to dig a canal $12 \, km$ long in $350 \, days$ and employs $45$ men. After $200 \, days$ he finds that only $4.5 \, km$ of the canal has been completed. Find the number of extra men he must employ to finish the work in time (in $men$).

If $10$ persons can do a job in $20$ days,then $20$ persons with twice the efficiency can do the same job in (in days)

$A$ can do a piece of work in $30$ days while $B$ can do it in $40$ days. In how many days can $A$ and $B$ working together do it?