The figure shows a tank made up of 3 sections. Cuboid W with a square base of side 14 cm and height 41 cm. Cube X with a side of 10 cm. Cuboid Y that is 79 cm by 15 cm by 43 cm. Water from a tap above flows down at a rate of 2.8 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 tank to a height of 64 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of X
= 10 x 10 x 10
= 1000 cm³ 

Volume of Y
= 79 x 15 x 43
= 50955 cm³ 

1 ℓ = 1000 cm³ 
2.8 ℓ = 2800 cm³ 

Net increase in volume per minute
= 2800 - 1000
= 1800 cm³/min

Height of W to be filled with water
= 64 - (43 + 10)
= 11 cm

Volume of water in W
= 14 x 14 x 11
= 2156 cm³ 

Volume of water in Y, X and part of W
= 50955 + 1000 + 2156
= 54111 cm³ 

Time taken to reach height
= 54111 ÷ 1800
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min