One pipe can fill a tank three times as fast as another

One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, the slower pipe alone will be able to fill the tank in

Let time taken by faster pipe be t minutes.
From the question ,

∴	1	+	1	=	1
	t		3t		36

⇒	3 + 1	=	1
	3t		36

⇒ 3t = 36 × 4
⇒ t = 48
∴ Time taken by slower pipe to fill the tank = 3t = 3 × 48 = 144 minutes