The figure shows a tank made up of 3 sections. Cuboid U with a square base of side 25 cm and height 33 cm. Cube V with a side of 10 cm. Cuboid W that is 75 cm by 13 cm by 42 cm. Water from a tap above flows down at a rate of 3.1 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 60 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of V
= 10 x 10 x 10
= 1000 cm³ 

Volume of W
= 75 x 13 x 42
= 40950 cm³ 

2 ℓ = 2000 cm³ 
3.1 ℓ = 3100 cm³ 

Net increase in volume per minute
= 3100 - 2000
= 1100 cm³/min

Height of U to be filled with water
= 60 - (42 + 10)
= 8 cm

Volume of water in U
= 25 x 25 x 8
= 5000 cm³ 

Volume of water in W, V and part of U
= 40950 + 1000 + 5000
= 46950 cm³ 

Time taken to reach height
= 46950 ÷ 1100
≈ 43 min (Correct to nearest whole number)

Answer(s): 43 min