The figure shows a tank made up of 3 sections. Cuboid F with a square base of side 25 cm and height 35 cm. Cube G with a side of 14 cm. Cuboid H that is 72 cm by 21 cm by 40 cm. Water from a tap above flows down at a rate of 3.6 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 G
= 14 x 14 x 14
= 2744 cm³ 

Volume of H
= 72 x 21 x 40
= 60480 cm³ 

2 ℓ = 2000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 2000
= 1600 cm³/min

Height of F to be filled with water
= 64 - (40 + 14)
= 10 cm

Volume of water in F
= 25 x 25 x 10
= 6250 cm³ 

Volume of water in H, G and part of F
= 60480 + 2744 + 6250
= 69474 cm³ 

Time taken to reach height
= 69474 ÷ 1600
≈ 43 min (Correct to nearest whole number)

Answer(s): 43 min