The figure shows a container made up of 3 sections. Cuboid Z with a square base of side 9 cm and height 21 cm. Cube A with a side of 16 cm. Cuboid B that is 60 cm by 21 cm by 44 cm. Water from a tap above flows down at a rate of 3.1 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 A
= 16 x 16 x 16
= 4096 cm³ 

Volume of B
= 60 x 21 x 44
= 55440 cm³ 

1 ℓ = 1000 cm³ 
3.1 ℓ = 3100 cm³ 

Net increase in volume per minute
= 3100 - 1000
= 2100 cm³/min

Height of Z to be filled with water
= 68 - (44 + 16)
= 8 cm

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

Volume of water in B, A and part of Z
= 55440 + 4096 + 648
= 60184 cm³ 

Time taken to reach height
= 60184 ÷ 2100
≈ 29 min (Correct to nearest whole number)

Answer(s): 29 min