An empty rectangular tank has a capacity of 138 ℓ and a height of 20 cm. At 10 a.m., Tap J is turned on to fill the tank at a rate of 8 ℓ per minute for 17 minutes. After 2 minutes, Tap K 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 
8 ℓ = 8000 cm³ 
6 ℓ = 6000 cm³ 
138 ℓ = 138000 cm³

Volume of water flowed in from Tap J
= 17 x 8000
= 136000 cm³

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

Volume of water left in the tank
= 136000 - 102000
= 34000 cm³

Base area of the tank
= 138000 ÷ 20
= 6900 cm² 

Height of water left in the tank
= 34000 ÷ 6900
≈ 4.9 cm

Answer(s): 4.9 cm