The figure shows a tank made up of 3 sections. Cuboid U with a square base of side 9 cm and height 33 cm. Cube V with a side of 11 cm. Cuboid W that is 77 cm by 22 cm by 45 cm. Water from a tap above flows down at a rate of 3.7 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 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of V
= 11 x 11 x 11
= 1331 cm³ 

Volume of W
= 77 x 22 x 45
= 76230 cm³ 

1 ℓ = 1000 cm³ 
3.7 ℓ = 3700 cm³ 

Net increase in volume per minute
= 3700 - 1000
= 2700 cm³/min

Height of U to be filled with water
= 70 - (45 + 11)
= 14 cm

Volume of water in U
= 9 x 9 x 14
= 1134 cm³ 

Volume of water in W, V and part of U
= 76230 + 1331 + 1134
= 78695 cm³ 

Time taken to reach height
= 78695 ÷ 2700
≈ 29 min (Correct to nearest whole number)

Answer(s): 29 min