The figure shows a tank made up of 3 sections. Cuboid C with a square base of side 4 cm and height 21 cm. Cube D with a side of 12 cm. Cuboid E that is 68 cm by 15 cm by 48 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 tank to a height of 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of D
= 12 x 12 x 12
= 1728 cm³ 

Volume of E
= 68 x 15 x 48
= 48960 cm³ 

2 ℓ = 2000 cm³ 
3.6 ℓ = 3600 cm³ 

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

Height of C to be filled with water
= 66 - (48 + 12)
= 6 cm

Volume of water in C
= 4 x 4 x 6
= 96 cm³ 

Volume of water in E, D and part of C
= 48960 + 1728 + 96
= 50784 cm³ 

Time taken to reach height
= 50784 ÷ 1600
≈ 32 min (Correct to nearest whole number)

Answer(s): 32 min