The figure shows a tank made up of 3 sections. Cuboid N with a square base of side 9 cm and height 31 cm. Cube P with a side of 13 cm. Cuboid Q that is 75 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 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of P
= 13 x 13 x 13
= 2197 cm³ 

Volume of Q
= 75 x 15 x 41
= 46125 cm³ 

2 ℓ = 2000 cm³ 
2.7 ℓ = 2700 cm³ 

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

Height of N to be filled with water
= 66 - (41 + 13)
= 12 cm

Volume of water in N
= 9 x 9 x 12
= 972 cm³ 

Volume of water in Q, P and part of N
= 46125 + 2197 + 972
= 49294 cm³ 

Time taken to reach height
= 49294 ÷ 700
≈ 70 min (Correct to nearest whole number)

Answer(s): 70 min