F.4 Math 題唷= . =!!

The time(x min) required to boil a kettle of water varies directly as the volume (V cm^3) of water and inversely as the power(P W) of the stove.It is given that the volumes of two kettles of water are in the ratio 9:13 and the power of the stove used to boil them respectively are in the ratio 12:13.If 9 minutes is required to boil the first kettle of water,find the time required to boil the second kettle.

有人識計嗎...= =?