The figure, not drawn to scale, shows an empty container measuring 20 cm by 20 cm by 15 cm. Water flows from Tap L at a rate of 400 mℓ per minute and from Tap M at a rate of 240 mℓ per minute. Tower N and Tower P have a base area of 20 cm² and 30 cm² respectively. Water is drained out of the container at a rate of 150 mℓ per minute. Find the height of the water level after 13 minutes.
Volume of the container
= 20 x 20 x 15
= 6000 cm³ 

Volume of water flow per minute
= 400 + 240 - 150
= 490 cm³/min

Volume of water flow in 13 minutes
= 13 x 490
= 6370 cm³ 

Volume of water in the 2 towers
= 6370 - 6000
= 370 cm³ 

Total combined base areas of 2 towers
= 20 + 30
= 50 cm² 

Height of water in 2 towers
= 370 ÷ 50
= 7.4 cm

Total height of water
= 7.4 + 15
= 22.4 cm

Answer(s): 22.4 cm