The figure shows a tank made up of 3 sections. Cuboid B with a square base of side 9 cm and height 39 cm. Cube C with a side of 13 cm. Cuboid D that is 68 cm by 18 cm by 43 cm. Water from a tap above flows down at a rate of 3.3 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 tank to a height of 63 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
= 68 x 18 x 43
= 52632 cm³ 

1 ℓ = 1000 cm³ 
3.3 ℓ = 3300 cm³ 

Net increase in volume per minute
= 3300 - 1000
= 2300 cm³/min

Height of B to be filled with water
= 63 - (43 + 13)
= 7 cm

Volume of water in B
= 9 x 9 x 7
= 567 cm³ 

Volume of water in D, C and part of B
= 52632 + 2197 + 567
= 55396 cm³ 

Time taken to reach height
= 55396 ÷ 2300
≈ 24 min (Correct to nearest whole number)

Answer(s): 24 min