The figure shows a tank made up of 3 sections. Cuboid V with a square base of side 14 cm and height 27 cm. Cube W with a side of 14 cm. Cuboid X that is 77 cm by 11 cm by 48 cm. Water from a tap above flows down at a rate of 3.7 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 68 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of W
= 14 x 14 x 14
= 2744 cm³ 

Volume of X
= 77 x 11 x 48
= 40656 cm³ 

1 ℓ = 1000 cm³ 
3.7 ℓ = 3700 cm³ 

Net increase in volume per minute
= 3700 - 1000
= 2700 cm³/min

Height of V to be filled with water
= 68 - (48 + 14)
= 6 cm

Volume of water in V
= 14 x 14 x 6
= 1176 cm³ 

Volume of water in X, W and part of V
= 40656 + 2744 + 1176
= 44576 cm³ 

Time taken to reach height
= 44576 ÷ 2700
≈ 17 min (Correct to nearest whole number)

Answer(s): 17 min