The figure shows a container made up of 3 sections. Cuboid Q with a square base of side 25 cm and height 49 cm. Cube R with a side of 12 cm. Cuboid S that is 73 cm by 23 cm by 47 cm. Water from a tap above flows down at a rate of 2.7 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 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of R
= 12 x 12 x 12
= 1728 cm³ 

Volume of S
= 73 x 23 x 47
= 78913 cm³ 

1 ℓ = 1000 cm³ 
2.7 ℓ = 2700 cm³ 

Net increase in volume per minute
= 2700 - 1000
= 1700 cm³/min

Height of Q to be filled with water
= 70 - (47 + 12)
= 11 cm

Volume of water in Q
= 25 x 25 x 11
= 6875 cm³ 

Volume of water in S, R and part of Q
= 78913 + 1728 + 6875
= 87516 cm³ 

Time taken to reach height
= 87516 ÷ 1700
≈ 51 min (Correct to nearest whole number)

Answer(s): 51 min