The figure shows a tank made up of 3 sections. Cuboid G with a square base of side 14 cm and height 33 cm. Cube H with a side of 14 cm. Cuboid J that is 68 cm by 21 cm by 45 cm. Water from a tap above flows down at a rate of 3.9 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of H
= 14 x 14 x 14
= 2744 cm³ 

Volume of J
= 68 x 21 x 45
= 64260 cm³ 

1 ℓ = 1000 cm³ 
3.9 ℓ = 3900 cm³ 

Net increase in volume per minute
= 3900 - 1000
= 2900 cm³/min

Height of G to be filled with water
= 69 - (45 + 14)
= 10 cm

Volume of water in G
= 14 x 14 x 10
= 1960 cm³ 

Volume of water in J, H and part of G
= 64260 + 2744 + 1960
= 68964 cm³ 

Time taken to reach height
= 68964 ÷ 2900
≈ 24 min (Correct to nearest whole number)

Answer(s): 24 min