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

	Scenario 1		Scenario 2
Tank type	Tank F	Tank G	Tank F	Tank G
Volume of the tank	3 u	7 u - 6	3 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 = 3 p --- (1)
7 u - 6 = 6 p
7 u = 6 p + 6 --- (2)

Make u the same.

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

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

(3) = (4)
21 p = 18 p + 18
21 p - 18 p = 18
3 p = 18
1 p = 18 ÷ 3 = 6

Volume of Tank G
= 6 p
= 6 x 6
= 36 ℓ

Answer(s): 36 ℓ