The figure shows a tank made up of 3 sections. Cuboid E with a square base of side 25 cm and height 24 cm. Cube F with a side of 15 cm. Cuboid G that is 61 cm by 24 cm by 45 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of F
= 15 x 15 x 15
= 3375 cm³ 

Volume of G
= 61 x 24 x 45
= 65880 cm³ 

1 ℓ = 1000 cm³ 
2.4 ℓ = 2400 cm³ 

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

Height of E to be filled with water
= 69 - (45 + 15)
= 9 cm

Volume of water in E
= 25 x 25 x 9
= 5625 cm³ 

Volume of water in G, F and part of E
= 65880 + 3375 + 5625
= 74880 cm³ 

Time taken to reach height
= 74880 ÷ 1400
≈ 53 min (Correct to nearest whole number)

Answer(s): 53 min