The figure shows a tank made up of 3 sections. Cuboid K with a square base of side 4 cm and height 43 cm. Cube L with a side of 12 cm. Cuboid M that is 61 cm by 30 cm by 45 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 2 litre per minute. How long did it take to fill up the tank to a height of 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of L
= 12 x 12 x 12
= 1728 cm³ 

Volume of M
= 61 x 30 x 45
= 82350 cm³ 

2 ℓ = 2000 cm³ 
3.9 ℓ = 3900 cm³ 

Net increase in volume per minute
= 3900 - 2000
= 1900 cm³/min

Height of K to be filled with water
= 70 - (45 + 12)
= 13 cm

Volume of water in K
= 4 x 4 x 13
= 208 cm³ 

Volume of water in M, L and part of K
= 82350 + 1728 + 208
= 84286 cm³ 

Time taken to reach height
= 84286 ÷ 1900
≈ 44 min (Correct to nearest whole number)

Answer(s): 44 min