The figure shows a tank made up of 3 sections. Cuboid U with a square base of side 9 cm and height 24 cm. Cube V with a side of 16 cm. Cuboid W that is 78 cm by 12 cm by 40 cm. Water from a tap above flows down at a rate of 3.3 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 65 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of V
= 16 x 16 x 16
= 4096 cm³ 

Volume of W
= 78 x 12 x 40
= 37440 cm³ 

2 ℓ = 2000 cm³ 
3.3 ℓ = 3300 cm³ 

Net increase in volume per minute
= 3300 - 2000
= 1300 cm³/min

Height of U to be filled with water
= 65 - (40 + 16)
= 9 cm

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

Volume of water in W, V and part of U
= 37440 + 4096 + 729
= 42265 cm³ 

Time taken to reach height
= 42265 ÷ 1300
≈ 33 min (Correct to nearest whole number)

Answer(s): 33 min