The figure shows a tank made up of 3 sections. Cuboid X with a square base of side 14 cm and height 27 cm. Cube Y with a side of 15 cm. Cuboid Z that is 71 cm by 10 cm by 47 cm. Water from a tap above flows down at a rate of 3.8 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 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of Y
= 15 x 15 x 15
= 3375 cm³ 

Volume of Z
= 71 x 10 x 47
= 33370 cm³ 

1 ℓ = 1000 cm³ 
3.8 ℓ = 3800 cm³ 

Net increase in volume per minute
= 3800 - 1000
= 2800 cm³/min

Height of X to be filled with water
= 70 - (47 + 15)
= 8 cm

Volume of water in X
= 14 x 14 x 8
= 1568 cm³ 

Volume of water in Z, Y and part of X
= 33370 + 3375 + 1568
= 38313 cm³ 

Time taken to reach height
= 38313 ÷ 2800
≈ 14 min (Correct to nearest whole number)

Answer(s): 14 min