The figure shows a container made up of 3 sections. Cuboid B with a square base of side 4 cm and height 45 cm. Cube C with a side of 15 cm. Cuboid D that is 67 cm by 18 cm by 42 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 67 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of C
= 15 x 15 x 15
= 3375 cm³ 

Volume of D
= 67 x 18 x 42
= 50652 cm³ 

1 ℓ = 1000 cm³ 
2.8 ℓ = 2800 cm³ 

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

Height of B to be filled with water
= 67 - (42 + 15)
= 10 cm

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

Volume of water in D, C and part of B
= 50652 + 3375 + 160
= 54187 cm³ 

Time taken to reach height
= 54187 ÷ 1800
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min