The figure shows a tank made up of 3 sections. Cuboid W with a square base of side 25 cm and height 43 cm. Cube X with a side of 19 cm. Cuboid Y that is 69 cm by 12 cm by 41 cm. Water from a tap above flows down at a rate of 2.1 litres per minute while water is drained out from the bottom at a rate of 2 litre per minute. How long did it take to fill up the tank to a height of 67 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of X
= 19 x 19 x 19
= 6859 cm³ 

Volume of Y
= 69 x 12 x 41
= 33948 cm³ 

2 ℓ = 2000 cm³ 
2.1 ℓ = 2100 cm³ 

Net increase in volume per minute
= 2100 - 2000
= 100 cm³/min

Height of W to be filled with water
= 67 - (41 + 19)
= 7 cm

Volume of water in W
= 25 x 25 x 7
= 4375 cm³ 

Volume of water in Y, X and part of W
= 33948 + 6859 + 4375
= 45182 cm³ 

Time taken to reach height
= 45182 ÷ 100
≈ 452 min (Correct to nearest whole number)

Answer(s): 452 min