The figure shows a tank made up of 3 sections. Cuboid J with a square base of side 9 cm and height 32 cm. Cube K with a side of 17 cm. Cuboid L that is 62 cm by 19 cm by 40 cm. Water from a tap above flows down at a rate of 3.1 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 65 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of K
= 17 x 17 x 17
= 4913 cm³ 

Volume of L
= 62 x 19 x 40
= 47120 cm³ 

1 ℓ = 1000 cm³ 
3.1 ℓ = 3100 cm³ 

Net increase in volume per minute
= 3100 - 1000
= 2100 cm³/min

Height of J to be filled with water
= 65 - (40 + 17)
= 8 cm

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

Volume of water in L, K and part of J
= 47120 + 4913 + 648
= 52681 cm³ 

Time taken to reach height
= 52681 ÷ 2100
≈ 25 min (Correct to nearest whole number)

Answer(s): 25 min