The figure, not drawn to scale, shows an empty container measuring 20 cm by 15 cm by 15 cm. Water flows from Tap S at a rate of 300 mℓ per minute and from Tap T at a rate of 190 mℓ per minute. Tower U and Tower V have a base area of 30 cm² and 20 cm² respectively. Water is drained out of the container at a rate of 140 mℓ per minute. Find the height of the water level after 13 minutes.
Volume of the container
= 20 x 15 x 15
= 4500 cm³ 

Volume of water flow per minute
= 300 + 190 - 140
= 350 cm³/min

Volume of water flow in 13 minutes
= 13 x 350
= 4550 cm³ 

Volume of water in the 2 towers
= 4550 - 4500
= 50 cm³ 

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

Height of water in 2 towers
= 50 ÷ 50
= 1 cm

Total height of water
= 1 + 15
= 16 cm

Answer(s): 16 cm