There are two taps to fill a tank while a third to empty it. When the third tap is closed, they can fill the tank in 10 minutes and 12 minutes, respectively. If all the three taps be opened, the tank is filled in 15 minutes. If the first two taps are closed, in what time can the third tap empty the tank when it is full?
(a) $7 \mathrm{~min}$
(b) $9 \mathrm{~min}$ and $32 \mathrm{sec}$
(c) $8 \mathrm{~min}$ and $34 \mathrm{sec}$
(d) $6 \mathrm{~min}$.