3 pails and 2 tanks can hold 12.4 litres of water.
1 pail and 1 tank can hold 4.5 litres of water.

1. How many litres of water can 1 pail hold?
2. How many litres of water can 1 tank hold?
3. How many litres of water can 7 tanks hold?
4. How many litres of water can 4 tanks and 3 pails?

(a)
3 pails + 2 tanks = 12.4 --- (1)
1 pail + 1 tank = 4.5 --- (2)

(2) x 2
1 pail + 1 tank = 4.5
2 pails + 2 tanks = 4.5 x 2
2 pails + 2 tanks = 9 --- (3)

(1) - (3)
(3 pails + 2 tanks) - (2 pails + 2 tanks) = 12.4 - 9
3 pails + 2 tanks - 2 pails - 2 tanks = 3.4
3 pails - 2 pails + 2 tanks - 2 tanks = 3.4

1 pail = 3.4

Volume of 1 pail = 3.4 ℓ

(b)
Substitute 1 pail = 3.4 into (2).
1 pail + 1 tank = 4.5
3.4 + 1 tank = 4.5

1 tank = 4.5 - 3.4 = 1.1

Volume of 1 tank = 1.1 ℓ

(c)
Volume of 7 tanks
= 7 x 1.1
= 7.7 ℓ

(d)
Volume of 4 tanks and 3 pails
= 4 x 1.1 + 3 x 3.4
= 4.4 + 10.2
= 14.6 ℓ

Answer(s): (a) 3.4 ℓ; (b) 1.1 ℓ; (c) 7.7 ℓ; (d) 14.6 ℓ