The figure, not drawn to scale, shows an empty tank measuring 20 cm by 15 cm by 20 cm. Water flows from Tap Y at a rate of 200 mℓ per minute and from Tap Z at a rate of 240 mℓ per minute. Tower A and Tower B have a base area of 30 cm² and 50 cm² respectively. Water is drained out of the container at a rate of 120 mℓ per minute. Find the height of the water level after 19 minutes.
Volume of the tank
= 20 x 15 x 20
= 6000 cm³ 

Volume of water flow per minute
= 200 + 240 - 120
= 320 cm³/min

Volume of water flow in 19 minutes
= 19 x 320
= 6080 cm³ 

Volume of water in the 2 towers
= 6080 - 6000
= 80 cm³ 

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

Height of water in 2 towers
= 80 ÷ 80
= 1 cm

Total height of water
= 1 + 20
= 21 cm

Answer(s): 21 cm