The figure shows a tank made up of 3 sections. Cuboid Z with a square base of side 14 cm and height 46 cm. Cube A with a side of 12 cm. Cuboid B that is 66 cm by 17 cm by 48 cm. Water from a tap above flows down at a rate of 2.8 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of A
= 12 x 12 x 12
= 1728 cm³ 

Volume of B
= 66 x 17 x 48
= 53856 cm³ 

2 ℓ = 2000 cm³ 
2.8 ℓ = 2800 cm³ 

Net increase in volume per minute
= 2800 - 2000
= 800 cm³/min

Height of Z to be filled with water
= 68 - (48 + 12)
= 8 cm

Volume of water in Z
= 14 x 14 x 8
= 1568 cm³ 

Volume of water in B, A and part of Z
= 53856 + 1728 + 1568
= 57152 cm³ 

Time taken to reach height
= 57152 ÷ 800
≈ 71 min (Correct to nearest whole number)

Answer(s): 71 min