The figure, not drawn to scale, shows an empty tank measuring 20 cm by 15 cm by 30 cm. Water flows from Tap N at a rate of 500 mℓ per minute and from Tap P at a rate of 240 mℓ per minute. Tower Q and Tower R have a base area of 10 cm² and 50 cm² respectively. Water is drained out of the container at a rate of 140 mℓ per minute. Find the height of the water level after 17 minutes.
Volume of the tank
= 20 x 15 x 30
= 9000 cm³ 

Volume of water flow per minute
= 500 + 240 - 140
= 600 cm³/min

Volume of water flow in 17 minutes
= 17 x 600
= 10200 cm³ 

Volume of water in the 2 towers
= 10200 - 9000
= 1200 cm³ 

Total combined base areas of 2 towers
= 10 + 50
= 60 cm² 

Height of water in 2 towers
= 1200 ÷ 60
= 20 cm

Total height of water
= 20 + 30
= 50 cm

Answer(s): 50 cm