The figure shows a container made up of 3 sections. Cuboid M with a square base of side 25 cm and height 47 cm. Cube N with a side of 12 cm. Cuboid P that is 63 cm by 15 cm by 43 cm. Water from a tap above flows down at a rate of 3.6 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 63 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of N
= 12 x 12 x 12
= 1728 cm³ 

Volume of P
= 63 x 15 x 43
= 40635 cm³ 

2 ℓ = 2000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 2000
= 1600 cm³/min

Height of M to be filled with water
= 63 - (43 + 12)
= 8 cm

Volume of water in M
= 25 x 25 x 8
= 5000 cm³ 

Volume of water in P, N and part of M
= 40635 + 1728 + 5000
= 47363 cm³ 

Time taken to reach height
= 47363 ÷ 1600
≈ 30 min (Correct to nearest whole number)

Answer(s): 30 min