Pipe A and B running together can fill a cistern in $6$ min. If B takes $5$ min more than A to fill the cistern, then the times in which A and B will fill the cistern separately will be respectively:

Two pipes A and B can fill a tank in $36$ min and $45$ min respectively. Another pipe C can empty the tank in $30$ min. First A and B are opened. After $7$ min, C is also opened. The tank is filled up in:

Three taps A, B and C fill a tank in$20$ min, $15$ min and $12$ min respectively. If all the taps are opened simultaneously, how long will they take to fill $40\%$ of the tank?