An outlet pipe can empty a cistern in $3$ $h$. In what time (in $h$) will the pipe empty two-third part of the cistern?

$A$ reservoir is fitted with two pipes $A$ and $B$. Pipe $A$ can fill the reservoir $5$ $hours$ faster than pipe $B$. If both the pipes together fill the reservoir in $6$ $hours$,the reservoir will be filled by $A$ alone in:

$A$ pipe fills a water tank three times faster than another pipe. If the two pipes together can fill the empty tank in $36$ $minutes$,then how much time will the slower pipe alone take to fill the tank?

$A$ tank is filled in $5$ $hours$ by three pipes $A, B$ and $C$. Pipe $C$ is twice as fast as $B,$ and $B$ is twice as fast as $A$. How much time (in $hours$) will pipe $A$ alone take to fill the tank?

Two pipes $A$ and $B$ can fill a cistern in $15$ and $20$ $min$,respectively. Both the pipes are opened together,but after $2$ $min$,pipe $A$ is turned off. What is the total time (in $minutes$) required to fill the tank?

Two pipes $A$ and $B$ can separately fill a cistern in $60$ $minutes$ and $75$ $minutes$ respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened,then the cistern is full in $50$ $minutes$. In how much time (in $minutes$) can the third pipe alone empty the cistern?