The figure shows a container made up of 3 sections. Cuboid N with a square base of side 4 cm and height 27 cm. Cube P with a side of 14 cm. Cuboid Q that is 79 cm by 18 cm by 42 cm. Water from a tap above flows down at a rate of 3.2 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of P
= 14 x 14 x 14
= 2744 cm³ 

Volume of Q
= 79 x 18 x 42
= 59724 cm³ 

2 ℓ = 2000 cm³ 
3.2 ℓ = 3200 cm³ 

Net increase in volume per minute
= 3200 - 2000
= 1200 cm³/min

Height of N to be filled with water
= 69 - (42 + 14)
= 13 cm

Volume of water in N
= 4 x 4 x 13
= 208 cm³ 

Volume of water in Q, P and part of N
= 59724 + 2744 + 208
= 62676 cm³ 

Time taken to reach height
= 62676 ÷ 1200
≈ 52 min (Correct to nearest whole number)

Answer(s): 52 min