The figure shows a container made up of 3 sections. Cuboid F with a square base of side 9 cm and height 34 cm. Cube G with a side of 17 cm. Cuboid H that is 64 cm by 10 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 1 litre per minute. How long did it take to fill up the container to a height of 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of G
= 17 x 17 x 17
= 4913 cm³ 

Volume of H
= 64 x 10 x 43
= 27520 cm³ 

1 ℓ = 1000 cm³ 
3.5 ℓ = 3500 cm³ 

Net increase in volume per minute
= 3500 - 1000
= 2500 cm³/min

Height of F to be filled with water
= 68 - (43 + 17)
= 8 cm

Volume of water in F
= 9 x 9 x 8
= 648 cm³ 

Volume of water in H, G and part of F
= 27520 + 4913 + 648
= 33081 cm³ 

Time taken to reach height
= 33081 ÷ 2500
≈ 13 min (Correct to nearest whole number)

Answer(s): 13 min