The figure shows a container made up of 3 sections. Cuboid N with a square base of side 9 cm and height 24 cm. Cube P with a side of 18 cm. Cuboid Q that is 80 cm by 15 cm by 42 cm. Water from a tap above flows down at a rate of 2.6 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 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of P
= 18 x 18 x 18
= 5832 cm³ 

Volume of Q
= 80 x 15 x 42
= 50400 cm³ 

2 ℓ = 2000 cm³ 
2.6 ℓ = 2600 cm³ 

Net increase in volume per minute
= 2600 - 2000
= 600 cm³/min

Height of N to be filled with water
= 69 - (42 + 18)
= 9 cm

Volume of water in N
= 9 x 9 x 9
= 729 cm³ 

Volume of water in Q, P and part of N
= 50400 + 5832 + 729
= 56961 cm³ 

Time taken to reach height
= 56961 ÷ 600
≈ 95 min (Correct to nearest whole number)

Answer(s): 95 min