The figure shows a container made up of 3 sections. Cuboid B with a square base of side 25 cm and height 31 cm. Cube C with a side of 13 cm. Cuboid D that is 75 cm by 11 cm by 40 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 1 litre per minute. How long did it take to fill up the container to a height of 61 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of C
= 13 x 13 x 13
= 2197 cm³ 

Volume of D
= 75 x 11 x 40
= 33000 cm³ 

1 ℓ = 1000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 1000
= 2600 cm³/min

Height of B to be filled with water
= 61 - (40 + 13)
= 8 cm

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

Volume of water in D, C and part of B
= 33000 + 2197 + 5000
= 40197 cm³ 

Time taken to reach height
= 40197 ÷ 2600
≈ 15 min (Correct to nearest whole number)

Answer(s): 15 min