The figure shows a container made up of 3 sections. Cuboid X with a square base of side 9 cm and height 20 cm. Cube Y with a side of 16 cm. Cuboid Z that is 73 cm by 27 cm by 45 cm. Water from a tap above flows down at a rate of 2.5 litres per minute while water is drained out from the bottom at a rate of 2 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 Y
= 16 x 16 x 16
= 4096 cm³ 

Volume of Z
= 73 x 27 x 45
= 88695 cm³ 

2 ℓ = 2000 cm³ 
2.5 ℓ = 2500 cm³ 

Net increase in volume per minute
= 2500 - 2000
= 500 cm³/min

Height of X to be filled with water
= 68 - (45 + 16)
= 7 cm

Volume of water in X
= 9 x 9 x 7
= 567 cm³ 

Volume of water in Z, Y and part of X
= 88695 + 4096 + 567
= 93358 cm³ 

Time taken to reach height
= 93358 ÷ 500
≈ 187 min (Correct to nearest whole number)

Answer(s): 187 min