Risa has 2 tanks. Tank H and Tank J are of different capacities. If Tank H is filled by a tap at a rate of 3 litres per minute and Tank J is filled by a tap at a rate of 7 litres per minute, when Tank H is completely filled, 6 litres of water flowed out from Tank J. If Tank H is filled by a tap at a rate of 6 litres per minute and Tank J is filled by a tap at a rate of 2 litres per minute, when Tank H is completely filled, Tank J is only one-fifth-filled. What is the capacity of Tank J? Express your answer in litres.

	Scenario 1		Scenario 2
Tank type	Tank H	Tank J	Tank H	Tank J
Volume of the tank	3 u	7 u - 6	6 p	2 p x 5 = 10 p

Let 1 u be the time taken for Scenario 1.
Let 1 p be the time taken for Scenario 2.

3 u = 6 p --- (1)
7 u - 6 = 10 p
7 u = 10 p + 6 --- (2)

Make u the same.

(1) x 7
21 u = 42 p --- (3)

(2) x 3
21 u = 30 p + 18 --- (4)

(3) = (4)
42 p = 30 p + 18
42 p - 30 p = 18
12 p = 18
1 p = 18 ÷ 12 = 1.5

Volume of Tank J
= 10 p
= 10 x 1.5
= 15 ℓ

Answer(s): 15 ℓ