The figure shows a tank made up of 3 sections. Cuboid E with a square base of side 14 cm and height 28 cm. Cube F with a side of 12 cm. Cuboid G that is 68 cm by 14 cm by 43 cm. Water from a tap above flows down at a rate of 3.5 litres per minute while water is drained out from the bottom at a rate of 2 litre per minute. How long did it take to fill up the tank to a height of 64 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of F
= 12 x 12 x 12
= 1728 cm³ 

Volume of G
= 68 x 14 x 43
= 40936 cm³ 

2 ℓ = 2000 cm³ 
3.5 ℓ = 3500 cm³ 

Net increase in volume per minute
= 3500 - 2000
= 1500 cm³/min

Height of E to be filled with water
= 64 - (43 + 12)
= 9 cm

Volume of water in E
= 14 x 14 x 9
= 1764 cm³ 

Volume of water in G, F and part of E
= 40936 + 1728 + 1764
= 44428 cm³ 

Time taken to reach height
= 44428 ÷ 1500
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min