The figure shows a container made up of 3 sections. Cuboid K with a square base of side 9 cm and height 20 cm. Cube L with a side of 16 cm. Cuboid M that is 77 cm by 15 cm by 41 cm. Water from a tap above flows down at a rate of 3.7 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 67 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of L
= 16 x 16 x 16
= 4096 cm³ 

Volume of M
= 77 x 15 x 41
= 47355 cm³ 

1 ℓ = 1000 cm³ 
3.7 ℓ = 3700 cm³ 

Net increase in volume per minute
= 3700 - 1000
= 2700 cm³/min

Height of K to be filled with water
= 67 - (41 + 16)
= 10 cm

Volume of water in K
= 9 x 9 x 10
= 810 cm³ 

Volume of water in M, L and part of K
= 47355 + 4096 + 810
= 52261 cm³ 

Time taken to reach height
= 52261 ÷ 2700
≈ 19 min (Correct to nearest whole number)

Answer(s): 19 min