The figure shows a container made up of 3 sections. Cuboid W with a square base of side 25 cm and height 21 cm. Cube X with a side of 12 cm. Cuboid Y that is 60 cm by 23 cm by 46 cm. Water from a tap above flows down at a rate of 2.3 litres per minute while water is drained out from the bottom at a rate of 1 litre per minute. How long did it take to fill up the container to a height of 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of X
= 12 x 12 x 12
= 1728 cm³ 

Volume of Y
= 60 x 23 x 46
= 63480 cm³ 

1 ℓ = 1000 cm³ 
2.3 ℓ = 2300 cm³ 

Net increase in volume per minute
= 2300 - 1000
= 1300 cm³/min

Height of W to be filled with water
= 68 - (46 + 12)
= 10 cm

Volume of water in W
= 25 x 25 x 10
= 6250 cm³ 

Volume of water in Y, X and part of W
= 63480 + 1728 + 6250
= 71458 cm³ 

Time taken to reach height
= 71458 ÷ 1300
≈ 55 min (Correct to nearest whole number)

Answer(s): 55 min