The figure, not drawn to scale, shows an empty container measuring 20 cm by 15 cm by 25 cm. Water flows from Tap Q at a rate of 500 mℓ per minute and from Tap R at a rate of 180 mℓ per minute. Tower S and Tower T have a base area of 20 cm² and 40 cm² respectively. Water is drained out of the container at a rate of 160 mℓ per minute. Find the height of the water level after 15 minutes.
Volume of the container
= 20 x 15 x 25
= 7500 cm³ 

Volume of water flow per minute
= 500 + 180 - 160
= 520 cm³/min

Volume of water flow in 15 minutes
= 15 x 520
= 7800 cm³ 

Volume of water in the 2 towers
= 7800 - 7500
= 300 cm³ 

Total combined base areas of 2 towers
= 20 + 40
= 60 cm² 

Height of water in 2 towers
= 300 ÷ 60
= 5 cm

Total height of water
= 5 + 25
= 30 cm

Answer(s): 30 cm