The figure shows a tank made up of 3 sections. Cuboid Z with a square base of side 4 cm and height 24 cm. Cube A with a side of 13 cm. Cuboid B that is 79 cm by 12 cm by 50 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 tank to a height of 69 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of A
= 13 x 13 x 13
= 2197 cm³ 

Volume of B
= 79 x 12 x 50
= 47400 cm³ 

1 ℓ = 1000 cm³ 
3.7 ℓ = 3700 cm³ 

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

Height of Z to be filled with water
= 69 - (50 + 13)
= 6 cm

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

Volume of water in B, A and part of Z
= 47400 + 2197 + 96
= 49693 cm³ 

Time taken to reach height
= 49693 ÷ 2700
≈ 18 min (Correct to nearest whole number)

Answer(s): 18 min