The figure shows a container made up of 3 sections. Cuboid Q with a square base of side 9 cm and height 36 cm. Cube R with a side of 11 cm. Cuboid S that is 72 cm by 14 cm by 45 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 2 litre per minute. How long did it take to fill up the container to a height of 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of R
= 11 x 11 x 11
= 1331 cm³ 

Volume of S
= 72 x 14 x 45
= 45360 cm³ 

2 ℓ = 2000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 2000
= 1600 cm³/min

Height of Q to be filled with water
= 70 - (45 + 11)
= 14 cm

Volume of water in Q
= 9 x 9 x 14
= 1134 cm³ 

Volume of water in S, R and part of Q
= 45360 + 1331 + 1134
= 47825 cm³ 

Time taken to reach height
= 47825 ÷ 1600
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min