The figure shows a container made up of 3 sections. Cuboid J with a square base of side 4 cm and height 21 cm. Cube K with a side of 18 cm. Cuboid L that is 73 cm by 26 cm by 40 cm. Water from a tap above flows down at a rate of 2.8 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 K
= 18 x 18 x 18
= 5832 cm³ 

Volume of L
= 73 x 26 x 40
= 75920 cm³ 

1 ℓ = 1000 cm³ 
2.8 ℓ = 2800 cm³ 

Net increase in volume per minute
= 2800 - 1000
= 1800 cm³/min

Height of J to be filled with water
= 68 - (40 + 18)
= 10 cm

Volume of water in J
= 4 x 4 x 10
= 160 cm³ 

Volume of water in L, K and part of J
= 75920 + 5832 + 160
= 81912 cm³ 

Time taken to reach height
= 81912 ÷ 1800
≈ 46 min (Correct to nearest whole number)

Answer(s): 46 min