A sentence has been given in Active/Passive Voice. Out of the four given alternatives, select the one which best expresses the same sentence inPassive/Active Voice.
Pipe A can fill an empty cistern in 4 hours while along with Pipe B it can fill it up in 3 hours. Only Pipe A is turned on for an hour after which Pipe B is also turned on. How much total time will it take to fill up the cistern?