The figure is not drawn to scale. Tank B measuring 54 cm by 42 cm by 25 cm contained 30.12 ℓ of water. Tank C measuring 40 cm by 31 cm by 37 cm contained 31 ℓ of water. Valen poured some water from Tank B into Tank C without spilling and the water level of Tank C rose to 31 cm. What was the height of water level left in Tank B?
1 ℓ = 1000 cm³
31 ℓ = 31000 cm³
30.12 ℓ = 30.12 x 1000 = 30120 cm³

Height of water in Tank C at first
= 31000 ÷ 40 ÷ 31
= 25 cm

Increase in the height of water in Tank C
= 31 - 25
= 6 cm

Volume of water poured into Tank C
= 40 x 31 x 6
= 7440 cm³ 

Volume of water left in Tank B
= 30120 - 7440
= 22680 cm³ 

Height of water left in Tank B
= 22680 ÷ 54 ÷ 42
= 10 cm

Answer(s): 10 cm