TS ICET 30 Sep 2020 Shift 2 Paper

A pipe can fill a tank in 16 minutes and a second one fill it in 24 minutes. A third pipe can empty that full tank in 8 minutes. The first two pipes are kept open for 4 minutes in the beginning and then the third pipe is opened. Then the time in which the tank will be emptied after all the three pipes started working simultaneously ( in minutes)?