The figure shows a container made up of 3 sections. Cuboid U with a square base of side 25 cm and height 33 cm. Cube V with a side of 11 cm. Cuboid W that is 78 cm by 25 cm by 42 cm. Water from a tap above flows down at a rate of 3.8 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of V
= 11 x 11 x 11
= 1331 cm³ 

Volume of W
= 78 x 25 x 42
= 81900 cm³ 

1 ℓ = 1000 cm³ 
3.8 ℓ = 3800 cm³ 

Net increase in volume per minute
= 3800 - 1000
= 2800 cm³/min

Height of U to be filled with water
= 69 - (42 + 11)
= 16 cm

Volume of water in U
= 25 x 25 x 16
= 10000 cm³ 

Volume of water in W, V and part of U
= 81900 + 1331 + 10000
= 93231 cm³ 

Time taken to reach height
= 93231 ÷ 2800
≈ 33 min (Correct to nearest whole number)

Answer(s): 33 min