The figure shows a tank made up of 3 sections. Cuboid F with a square base of side 14 cm and height 21 cm. Cube G with a side of 11 cm. Cuboid H that is 66 cm by 19 cm by 44 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
= 11 x 11 x 11
= 1331 cm³ 

Volume of H
= 66 x 19 x 44
= 55176 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 - (44 + 11)
= 9 cm

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

Volume of water in H, G and part of F
= 55176 + 1331 + 1764
= 58271 cm³ 

Time taken to reach height
= 58271 ÷ 1600
≈ 36 min (Correct to nearest whole number)

Answer(s): 36 min