The figure, not drawn to scale, shows an empty tank measuring 20 cm by 20 cm by 15 cm. Water flows from Tap N at a rate of 400 mℓ per minute and from Tap P at a rate of 170 mℓ per minute. Tower Q and Tower R have a base area of 20 cm² and 20 cm² respectively. Water is drained out of the container at a rate of 130 mℓ per minute. Find the height of the water level after 19 minutes.
Volume of the tank
= 20 x 20 x 15
= 6000 cm³ 

Volume of water flow per minute
= 400 + 170 - 130
= 440 cm³/min

Volume of water flow in 19 minutes
= 19 x 440
= 8360 cm³ 

Volume of water in the 2 towers
= 8360 - 6000
= 2360 cm³ 

Total combined base areas of 2 towers
= 20 + 20
= 40 cm² 

Height of water in 2 towers
= 2360 ÷ 40
= 59 cm

Total height of water
= 59 + 15
= 74 cm

Answer(s): 74 cm