The figure shows a tank made up of 3 sections. Cuboid K with a square base of side 4 cm and height 38 cm. Cube L with a side of 16 cm. Cuboid M that is 80 cm by 15 cm by 41 cm. Water from a tap above flows down at a rate of 2.7 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 L
= 16 x 16 x 16
= 4096 cm³ 

Volume of M
= 80 x 15 x 41
= 49200 cm³ 

2 ℓ = 2000 cm³ 
2.7 ℓ = 2700 cm³ 

Net increase in volume per minute
= 2700 - 2000
= 700 cm³/min

Height of K to be filled with water
= 65 - (41 + 16)
= 8 cm

Volume of water in K
= 4 x 4 x 8
= 128 cm³ 

Volume of water in M, L and part of K
= 49200 + 4096 + 128
= 53424 cm³ 

Time taken to reach height
= 53424 ÷ 700
≈ 76 min (Correct to nearest whole number)

Answer(s): 76 min