The figure shows a tank made up of 3 sections. Cuboid J with a square base of side 9 cm and height 46 cm. Cube K with a side of 11 cm. Cuboid L that is 72 cm by 18 cm by 45 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 2 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
= 11 x 11 x 11
= 1331 cm³ 

Volume of L
= 72 x 18 x 45
= 58320 cm³ 

2 ℓ = 2000 cm³ 
3.1 ℓ = 3100 cm³ 

Net increase in volume per minute
= 3100 - 2000
= 1100 cm³/min

Height of J to be filled with water
= 65 - (45 + 11)
= 9 cm

Volume of water in J
= 9 x 9 x 9
= 729 cm³ 

Volume of water in L, K and part of J
= 58320 + 1331 + 729
= 60380 cm³ 

Time taken to reach height
= 60380 ÷ 1100
≈ 55 min (Correct to nearest whole number)

Answer(s): 55 min