The figure shows a tank made up of 3 sections. Cuboid G with a square base of side 9 cm and height 20 cm. Cube H with a side of 15 cm. Cuboid J that is 68 cm by 14 cm by 40 cm. Water from a tap above flows down at a rate of 2.4 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 62 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of H
= 15 x 15 x 15
= 3375 cm³ 

Volume of J
= 68 x 14 x 40
= 38080 cm³ 

1 ℓ = 1000 cm³ 
2.4 ℓ = 2400 cm³ 

Net increase in volume per minute
= 2400 - 1000
= 1400 cm³/min

Height of G to be filled with water
= 62 - (40 + 15)
= 7 cm

Volume of water in G
= 9 x 9 x 7
= 567 cm³ 

Volume of water in J, H and part of G
= 38080 + 3375 + 567
= 42022 cm³ 

Time taken to reach height
= 42022 ÷ 1400
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min