An empty rectangular container has a capacity of 166 ℓ and a height of 20 cm. At 8 a.m., Tap Q is turned on to fill the container at a rate of 6 ℓ per minute for 15 minutes. After 6 minutes, Tap R is turned on to drain water from the container at a rate of 5 ℓ per minute for 7 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 
6 ℓ = 6000 cm³ 
5 ℓ = 5000 cm³ 
166 ℓ = 166000 cm³

Volume of water flowed in from Tap Q
= 15 x 6000
= 90000 cm³

Volume of water from drained from Tap R
= 7 x 5000
= 35000 cm³

Volume of water left in the container
= 90000 - 35000
= 55000 cm³

Base area of the container
= 166000 ÷ 20
= 8300 cm² 

Height of water left in the container
= 55000 ÷ 8300
≈ 6.6 cm

Answer(s): 6.6 cm