$P$ and $Q$ working together can complete a certain work in $6 \, \text{days}$. $Q$ alone can do it in $8 \, \text{days}$. In how many $\text{days}$ could $P$ alone finish the same work?

$A$ 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 $men$).

$2$ men and $1$ woman can do a piece of work in $14$ days,while $4$ women and $2$ men can do the same work in $8$ days. If a man gets $Rs. 90$ per day,what should be the wages per day of a woman? (in $Rs.$)

$A$ 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?

$A$ man can do a piece of work in $5$ days,but with the help of his son,he can do it in $3$ days. In what time can the son do it alone? (in days)

$A$ does half as much work as $B$ in $\frac{3}{4}$ of the time. If together they take $18 \text{ days}$ to complete a work,how much time shall $B$ take to do it alone? (in $\text{days}$)