The figure shows a container made up of 3 sections. Cuboid P with a square base of side 25 cm and height 22 cm. Cube Q with a side of 17 cm. Cuboid R that is 79 cm by 22 cm by 40 cm. Water from a tap above flows down at a rate of 3.3 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 Q
= 17 x 17 x 17
= 4913 cm³ 

Volume of R
= 79 x 22 x 40
= 69520 cm³ 

1 ℓ = 1000 cm³ 
3.3 ℓ = 3300 cm³ 

Net increase in volume per minute
= 3300 - 1000
= 2300 cm³/min

Height of P to be filled with water
= 70 - (40 + 17)
= 13 cm

Volume of water in P
= 25 x 25 x 13
= 8125 cm³ 

Volume of water in R, Q and part of P
= 69520 + 4913 + 8125
= 82558 cm³ 

Time taken to reach height
= 82558 ÷ 2300
≈ 36 min (Correct to nearest whole number)

Answer(s): 36 min