The figure shows a tank made up of 3 sections. Cuboid J with a square base of side 9 cm and height 29 cm. Cube K with a side of 10 cm. Cuboid L that is 69 cm by 27 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 2 litre per minute. How long did it take to fill up the tank to a height of 58 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of K
= 10 x 10 x 10
= 1000 cm³ 

Volume of L
= 69 x 27 x 40
= 74520 cm³ 

2 ℓ = 2000 cm³ 
3.4 ℓ = 3400 cm³ 

Net increase in volume per minute
= 3400 - 2000
= 1400 cm³/min

Height of J to be filled with water
= 58 - (40 + 10)
= 8 cm

Volume of water in J
= 9 x 9 x 8
= 648 cm³ 

Volume of water in L, K and part of J
= 74520 + 1000 + 648
= 76168 cm³ 

Time taken to reach height
= 76168 ÷ 1400
≈ 54 min (Correct to nearest whole number)

Answer(s): 54 min