Salik has 2 tanks. Tank Y and Tank Z are of different capacities. If Tank Y is filled by a tap at a rate of 3 litres per minute and Tank Z is filled by a tap at a rate of 7 litres per minute, when Tank Y is completely filled, 7 litres of water flowed out from Tank Z. If Tank Y is filled by a tap at a rate of 4 litres per minute and Tank Z is filled by a tap at a rate of 3 litres per minute, when Tank Y is completely filled, Tank Z is only half-filled. What is the capacity of Tank Z? Express your answer in litres.

	Scenario 1		Scenario 2
Tank type	Tank Y	Tank Z	Tank Y	Tank Z
Volume of the tank	3 u	7 u - 7	4 p	3 p x 2 = 6 p

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

3 u = 4 p --- (1)
7 u - 7 = 6 p
7 u = 6 p + 7 --- (2)

Make u the same.

(1) x 7
21 u = 28 p --- (3)

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

(3) = (4)
28 p = 18 p + 21
28 p - 18 p = 21
10 p = 21
1 p = 21 ÷ 10 = 2.1

Volume of Tank Z
= 6 p
= 6 x 2.1
= 12.6 ℓ

Answer(s): 12.6 ℓ