The figure, not drawn to scale, shows an empty tank measuring 30 cm by 20 cm by 15 cm. Water flows from Tap G at a rate of 500 mℓ per minute and from Tap H at a rate of 190 mℓ per minute. Tower J and Tower K have a base area of 40 cm² and 60 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 17 minutes.
Volume of the tank
= 30 x 20 x 15
= 9000 cm³ 

Volume of water flow per minute
= 500 + 190 - 120
= 570 cm³/min

Volume of water flow in 17 minutes
= 17 x 570
= 9690 cm³ 

Volume of water in the 2 towers
= 9690 - 9000
= 690 cm³ 

Total combined base areas of 2 towers
= 40 + 60
= 100 cm² 

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

Total height of water
= 6.9 + 15
= 21.9 cm

Answer(s): 21.9 cm