The figure, not drawn to scale, shows an empty container measuring 20 cm by 15 cm by 25 cm. Water flows from Tap C at a rate of 500 mℓ per minute and from Tap D at a rate of 240 mℓ per minute. Tower E and Tower F have a base area of 50 cm² and 50 cm² respectively. Water is drained out of the container at a rate of 110 mℓ per minute. Find the height of the water level after 13 minutes.
Volume of the container
= 20 x 15 x 25
= 7500 cm³ 

Volume of water flow per minute
= 500 + 240 - 110
= 630 cm³/min

Volume of water flow in 13 minutes
= 13 x 630
= 8190 cm³ 

Volume of water in the 2 towers
= 8190 - 7500
= 690 cm³ 

Total combined base areas of 2 towers
= 50 + 50
= 100 cm² 

Height of water in 2 towers
= 690 ÷ 100
= 6.9 cm

Total height of water
= 6.9 + 25
= 31.9 cm

Answer(s): 31.9 cm