The figure shows a tank made up of 3 sections. Cuboid U with a square base of side 9 cm and height 34 cm. Cube V with a side of 10 cm. Cuboid W that is 61 cm by 14 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 1 litre per minute. How long did it take to fill up the tank to a height of 61 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
= 61 x 14 x 41
= 35014 cm³ 

1 ℓ = 1000 cm³ 
2.1 ℓ = 2100 cm³ 

Net increase in volume per minute
= 2100 - 1000
= 1100 cm³/min

Height of U to be filled with water
= 61 - (41 + 10)
= 10 cm

Volume of water in U
= 9 x 9 x 10
= 810 cm³ 

Volume of water in W, V and part of U
= 35014 + 1000 + 810
= 36824 cm³ 

Time taken to reach height
= 36824 ÷ 1100
≈ 33 min (Correct to nearest whole number)

Answer(s): 33 min