The figure, not drawn to scale, shows an empty container measuring 20 cm by 15 cm by 20 cm. Water flows from Tap P at a rate of 400 mℓ per minute and from Tap Q at a rate of 240 mℓ per minute. Tower R and Tower S have a base area of 50 cm² and 30 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 19 minutes.
Volume of the container
= 20 x 15 x 20
= 6000 cm³ 

Volume of water flow per minute
= 400 + 240 - 140
= 500 cm³/min

Volume of water flow in 19 minutes
= 19 x 500
= 9500 cm³ 

Volume of water in the 2 towers
= 9500 - 6000
= 3500 cm³ 

Total combined base areas of 2 towers
= 50 + 30
= 80 cm² 

Height of water in 2 towers
= 3500 ÷ 80
= 43.75 cm

Total height of water
= 43.75 + 20
= 63.75 cm

Answer(s): 63.75 cm