The figure shows a tank made up of 3 sections. Cuboid K with a square base of side 25 cm and height 23 cm. Cube L with a side of 17 cm. Cuboid M that is 75 cm by 25 cm by 43 cm. Water from a tap above flows down at a rate of 2.3 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of L
= 17 x 17 x 17
= 4913 cm³ 

Volume of M
= 75 x 25 x 43
= 80625 cm³ 

2 ℓ = 2000 cm³ 
2.3 ℓ = 2300 cm³ 

Net increase in volume per minute
= 2300 - 2000
= 300 cm³/min

Height of K to be filled with water
= 68 - (43 + 17)
= 8 cm

Volume of water in K
= 25 x 25 x 8
= 5000 cm³ 

Volume of water in M, L and part of K
= 80625 + 4913 + 5000
= 90538 cm³ 

Time taken to reach height
= 90538 ÷ 300
≈ 302 min (Correct to nearest whole number)

Answer(s): 302 min