The figure shows a tank made up of 3 sections. Cuboid J with a square base of side 9 cm and height 43 cm. Cube K with a side of 15 cm. Cuboid L that is 65 cm by 24 cm by 43 cm. Water from a tap above flows down at a rate of 3.9 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
= 15 x 15 x 15
= 3375 cm³ 

Volume of L
= 65 x 24 x 43
= 67080 cm³ 

1 ℓ = 1000 cm³ 
3.9 ℓ = 3900 cm³ 

Net increase in volume per minute
= 3900 - 1000
= 2900 cm³/min

Height of J to be filled with water
= 69 - (43 + 15)
= 11 cm

Volume of water in J
= 9 x 9 x 11
= 891 cm³ 

Volume of water in L, K and part of J
= 67080 + 3375 + 891
= 71346 cm³ 

Time taken to reach height
= 71346 ÷ 2900
≈ 25 min (Correct to nearest whole number)

Answer(s): 25 min