The figure shows a tank made up of 3 sections. Cuboid J with a square base of side 25 cm and height 36 cm. Cube K with a side of 13 cm. Cuboid L that is 66 cm by 22 cm by 42 cm. Water from a tap above flows down at a rate of 2.7 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 K
= 13 x 13 x 13
= 2197 cm³ 

Volume of L
= 66 x 22 x 42
= 60984 cm³ 

1 ℓ = 1000 cm³ 
2.7 ℓ = 2700 cm³ 

Net increase in volume per minute
= 2700 - 1000
= 1700 cm³/min

Height of J to be filled with water
= 69 - (42 + 13)
= 14 cm

Volume of water in J
= 25 x 25 x 14
= 8750 cm³ 

Volume of water in L, K and part of J
= 60984 + 2197 + 8750
= 71931 cm³ 

Time taken to reach height
= 71931 ÷ 1700
≈ 42 min (Correct to nearest whole number)

Answer(s): 42 min