Rael has 2 containers. Container B and Container C are of different capacities. If Container B is filled by a tap at a rate of 3 litres per minute and Container C is filled by a tap at a rate of 7 litres per minute, when Container B is completely filled, 6 litres of water flowed out from Container C. If Container B is filled by a tap at a rate of 5 litres per minute and Container C is filled by a tap at a rate of 3 litres per minute, when Container B is completely filled, Container C is only one-third-filled. What is the capacity of Container C? Express your answer in litres.

	Scenario 1		Scenario 2
Container type	Container B	Container C	Container B	Container C
Volume of the container	3 u	7 u - 6	5 p	3 p x 3 = 9 p

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

3 u = 5 p --- (1)
7 u - 6 = 9 p
7 u = 9 p + 6 --- (2)

Make u the same.

(1) x 7
21 u = 35 p --- (3)

(2) x 3
21 u = 27 p + 18 --- (4)

(3) = (4)
35 p = 27 p + 18
35 p - 27 p = 18
8 p = 18
1 p = 18 ÷ 8 = 2.25

Volume of Container C
= 9 p
= 9 x 2.25
= 20.25 ℓ

Answer(s): 20.25 ℓ