The figure shows a tank made up of 3 sections. Cuboid V with a square base of side 9 cm and height 41 cm. Cube W with a side of 19 cm. Cuboid X that is 75 cm by 15 cm by 40 cm. Water from a tap above flows down at a rate of 2.5 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of W
= 19 x 19 x 19
= 6859 cm³ 

Volume of X
= 75 x 15 x 40
= 45000 cm³ 

2 ℓ = 2000 cm³ 
2.5 ℓ = 2500 cm³ 

Net increase in volume per minute
= 2500 - 2000
= 500 cm³/min

Height of V to be filled with water
= 68 - (40 + 19)
= 9 cm

Volume of water in V
= 9 x 9 x 9
= 729 cm³ 

Volume of water in X, W and part of V
= 45000 + 6859 + 729
= 52588 cm³ 

Time taken to reach height
= 52588 ÷ 500
≈ 105 min (Correct to nearest whole number)

Answer(s): 105 min