The figure shows a tank made up of 3 sections. Cuboid C with a square base of side 9 cm and height 31 cm. Cube D with a side of 13 cm. Cuboid E that is 62 cm by 23 cm by 43 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 2 litre per minute. How long did it take to fill up the tank to a height of 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of D
= 13 x 13 x 13
= 2197 cm³ 

Volume of E
= 62 x 23 x 43
= 61318 cm³ 

2 ℓ = 2000 cm³ 
3.7 ℓ = 3700 cm³ 

Net increase in volume per minute
= 3700 - 2000
= 1700 cm³/min

Height of C to be filled with water
= 70 - (43 + 13)
= 14 cm

Volume of water in C
= 9 x 9 x 14
= 1134 cm³ 

Volume of water in E, D and part of C
= 61318 + 2197 + 1134
= 64649 cm³ 

Time taken to reach height
= 64649 ÷ 1700
≈ 38 min (Correct to nearest whole number)

Answer(s): 38 min