The figure shows a container made up of 3 sections. Cuboid S with a square base of side 14 cm and height 49 cm. Cube T with a side of 20 cm. Cuboid U that is 80 cm by 17 cm by 41 cm. Water from a tap above flows down at a rate of 3.6 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 T
= 20 x 20 x 20
= 8000 cm³ 

Volume of U
= 80 x 17 x 41
= 55760 cm³ 

1 ℓ = 1000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 1000
= 2600 cm³/min

Height of S to be filled with water
= 68 - (41 + 20)
= 7 cm

Volume of water in S
= 14 x 14 x 7
= 1372 cm³ 

Volume of water in U, T and part of S
= 55760 + 8000 + 1372
= 65132 cm³ 

Time taken to reach height
= 65132 ÷ 2600
≈ 25 min (Correct to nearest whole number)

Answer(s): 25 min