The figure shows a container made up of 3 sections. Cuboid P with a square base of side 9 cm and height 38 cm. Cube Q with a side of 13 cm. Cuboid R that is 72 cm by 20 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of Q
= 13 x 13 x 13
= 2197 cm³ 

Volume of R
= 72 x 20 x 41
= 59040 cm³ 

1 ℓ = 1000 cm³ 
3.6 ℓ = 3600 cm³ 

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

Height of P to be filled with water
= 69 - (41 + 13)
= 15 cm

Volume of water in P
= 9 x 9 x 15
= 1215 cm³ 

Volume of water in R, Q and part of P
= 59040 + 2197 + 1215
= 62452 cm³ 

Time taken to reach height
= 62452 ÷ 2600
≈ 24 min (Correct to nearest whole number)

Answer(s): 24 min