The figure shows a container made up of 3 sections. Cuboid N with a square base of side 14 cm and height 48 cm. Cube P with a side of 10 cm. Cuboid Q that is 73 cm by 15 cm by 40 cm. Water from a tap above flows down at a rate of 2.1 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of P
= 10 x 10 x 10
= 1000 cm³ 

Volume of Q
= 73 x 15 x 40
= 43800 cm³ 

1 ℓ = 1000 cm³ 
2.1 ℓ = 2100 cm³ 

Net increase in volume per minute
= 2100 - 1000
= 1100 cm³/min

Height of N to be filled with water
= 68 - (40 + 10)
= 18 cm

Volume of water in N
= 14 x 14 x 18
= 3528 cm³ 

Volume of water in Q, P and part of N
= 43800 + 1000 + 3528
= 48328 cm³ 

Time taken to reach height
= 48328 ÷ 1100
≈ 44 min (Correct to nearest whole number)

Answer(s): 44 min