An empty rectangular tank has a capacity of 189 ℓ and a height of 35 cm. At 9 a.m., Tap Q is turned on to fill the tank at a rate of 10 ℓ per minute for 17 minutes. After 7 minutes, Tap R is turned on to drain water from the tank at a rate of 6 ℓ per minute for 17 minutes. What is the height of the water level in the tank in the end? Give the answer in 1 decimal place.
1 ℓ = 1000 cm³ 
10 ℓ = 10000 cm³ 
6 ℓ = 6000 cm³ 
189 ℓ = 189000 cm³

Volume of water flowed in from Tap Q
= 17 x 10000
= 170000 cm³

Volume of water from drained from Tap R
= 17 x 6000
= 102000 cm³

Volume of water left in the tank
= 170000 - 102000
= 68000 cm³

Base area of the tank
= 189000 ÷ 35
= 5400 cm² 

Height of water left in the tank
= 68000 ÷ 5400
≈ 12.6 cm

Answer(s): 12.6 cm