The figure shows a tank made up of 3 sections. Cuboid H with a square base of side 14 cm and height 42 cm. Cube J with a side of 20 cm. Cuboid K that is 78 cm by 10 cm by 40 cm. Water from a tap above flows down at a rate of 3.4 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 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of J
= 20 x 20 x 20
= 8000 cm³ 

Volume of K
= 78 x 10 x 40
= 31200 cm³ 

1 ℓ = 1000 cm³ 
3.4 ℓ = 3400 cm³ 

Net increase in volume per minute
= 3400 - 1000
= 2400 cm³/min

Height of H to be filled with water
= 66 - (40 + 20)
= 6 cm

Volume of water in H
= 14 x 14 x 6
= 1176 cm³ 

Volume of water in K, J and part of H
= 31200 + 8000 + 1176
= 40376 cm³ 

Time taken to reach height
= 40376 ÷ 2400
≈ 17 min (Correct to nearest whole number)

Answer(s): 17 min