The figure shows a container made up of 3 sections. Cuboid H with a square base of side 4 cm and height 37 cm. Cube J with a side of 13 cm. Cuboid K that is 78 cm by 24 cm by 40 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of J
= 13 x 13 x 13
= 2197 cm³ 

Volume of K
= 78 x 24 x 40
= 74880 cm³ 

1 ℓ = 1000 cm³ 
3.5 ℓ = 3500 cm³ 

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

Height of H to be filled with water
= 69 - (40 + 13)
= 16 cm

Volume of water in H
= 4 x 4 x 16
= 256 cm³ 

Volume of water in K, J and part of H
= 74880 + 2197 + 256
= 77333 cm³ 

Time taken to reach height
= 77333 ÷ 2500
≈ 31 min (Correct to nearest whole number)

Answer(s): 31 min