The figure shows a tank made up of 3 sections. Cuboid U with a square base of side 4 cm and height 37 cm. Cube V with a side of 13 cm. Cuboid W that is 76 cm by 20 cm by 45 cm. Water from a tap above flows down at a rate of 3.2 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 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of V
= 13 x 13 x 13
= 2197 cm³ 

Volume of W
= 76 x 20 x 45
= 68400 cm³ 

1 ℓ = 1000 cm³ 
3.2 ℓ = 3200 cm³ 

Net increase in volume per minute
= 3200 - 1000
= 2200 cm³/min

Height of U to be filled with water
= 66 - (45 + 13)
= 8 cm

Volume of water in U
= 4 x 4 x 8
= 128 cm³ 

Volume of water in W, V and part of U
= 68400 + 2197 + 128
= 70725 cm³ 

Time taken to reach height
= 70725 ÷ 2200
≈ 32 min (Correct to nearest whole number)

Answer(s): 32 min