The figure shows a container made up of 3 sections. Cuboid M with a square base of side 4 cm and height 39 cm. Cube N with a side of 16 cm. Cuboid P that is 71 cm by 23 cm by 45 cm. Water from a tap above flows down at a rate of 2.4 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of N
= 16 x 16 x 16
= 4096 cm³ 

Volume of P
= 71 x 23 x 45
= 73485 cm³ 

2 ℓ = 2000 cm³ 
2.4 ℓ = 2400 cm³ 

Net increase in volume per minute
= 2400 - 2000
= 400 cm³/min

Height of M to be filled with water
= 68 - (45 + 16)
= 7 cm

Volume of water in M
= 4 x 4 x 7
= 112 cm³ 

Volume of water in P, N and part of M
= 73485 + 4096 + 112
= 77693 cm³ 

Time taken to reach height
= 77693 ÷ 400
≈ 194 min (Correct to nearest whole number)

Answer(s): 194 min