The figure shows a container made up of 3 sections. Cuboid N with a square base of side 14 cm and height 27 cm. Cube P with a side of 19 cm. Cuboid Q that is 77 cm by 10 cm by 40 cm. Water from a tap above flows down at a rate of 3.6 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 container to a height of 70 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of P
= 19 x 19 x 19
= 6859 cm³ 

Volume of Q
= 77 x 10 x 40
= 30800 cm³ 

1 ℓ = 1000 cm³ 
3.6 ℓ = 3600 cm³ 

Net increase in volume per minute
= 3600 - 1000
= 2600 cm³/min

Height of N to be filled with water
= 70 - (40 + 19)
= 11 cm

Volume of water in N
= 14 x 14 x 11
= 2156 cm³ 

Volume of water in Q, P and part of N
= 30800 + 6859 + 2156
= 39815 cm³ 

Time taken to reach height
= 39815 ÷ 2600
≈ 15 min (Correct to nearest whole number)

Answer(s): 15 min