The figure shows a tank made up of 3 sections. Cuboid L with a square base of side 4 cm and height 26 cm. Cube M with a side of 12 cm. Cuboid N that is 74 cm by 20 cm by 41 cm. Water from a tap above flows down at a rate of 3.4 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 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of M
= 12 x 12 x 12
= 1728 cm³ 

Volume of N
= 74 x 20 x 41
= 60680 cm³ 

1 ℓ = 1000 cm³ 
3.4 ℓ = 3400 cm³ 

Net increase in volume per minute
= 3400 - 1000
= 2400 cm³/min

Height of L to be filled with water
= 66 - (41 + 12)
= 13 cm

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

Volume of water in N, M and part of L
= 60680 + 1728 + 208
= 62616 cm³ 

Time taken to reach height
= 62616 ÷ 2400
≈ 26 min (Correct to nearest whole number)

Answer(s): 26 min