An empty rectangular container has a capacity of 135 ℓ and a height of 18 cm. At 7 a.m., Tap A is turned on to fill the container at a rate of 5 ℓ per minute for 20 minutes. After 6 minutes, Tap B is turned on to drain water from the container at a rate of 3 ℓ per minute for 21 minutes. What is the height of the water level in the container in the end? Give the answer in 1 decimal place.
1 ℓ = 1000 cm³ 
5 ℓ = 5000 cm³ 
3 ℓ = 3000 cm³ 
135 ℓ = 135000 cm³

Volume of water flowed in from Tap A
= 20 x 5000
= 100000 cm³

Volume of water from drained from Tap B
= 21 x 3000
= 63000 cm³

Volume of water left in the container
= 100000 - 63000
= 37000 cm³

Base area of the container
= 135000 ÷ 18
= 7500 cm² 

Height of water left in the container
= 37000 ÷ 7500
≈ 4.9 cm

Answer(s): 4.9 cm