The figure shows a tank made up of 3 sections. Cuboid Q with a square base of side 14 cm and height 35 cm. Cube R with a side of 13 cm. Cuboid S that is 60 cm by 14 cm by 42 cm. Water from a tap above flows down at a rate of 2.4 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 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of R
= 13 x 13 x 13
= 2197 cm³ 

Volume of S
= 60 x 14 x 42
= 35280 cm³ 

1 ℓ = 1000 cm³ 
2.4 ℓ = 2400 cm³ 

Net increase in volume per minute
= 2400 - 1000
= 1400 cm³/min

Height of Q to be filled with water
= 70 - (42 + 13)
= 15 cm

Volume of water in Q
= 14 x 14 x 15
= 2940 cm³ 

Volume of water in S, R and part of Q
= 35280 + 2197 + 2940
= 40417 cm³ 

Time taken to reach height
= 40417 ÷ 1400
≈ 29 min (Correct to nearest whole number)

Answer(s): 29 min