An empty rectangular tank has a capacity of 168 ℓ and a height of 120 cm. At 10 a.m., Tap Q is turned on to fill the tank at a rate of 9 ℓ per minute for 18 minutes. After 13 minutes, Tap R is turned on to drain water from the tank at a rate of 3 ℓ per minute for 23 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 
9 ℓ = 9000 cm³ 
3 ℓ = 3000 cm³ 
168 ℓ = 168000 cm³

Volume of water flowed in from Tap Q
= 18 x 9000
= 162000 cm³

Volume of water from drained from Tap R
= 23 x 3000
= 69000 cm³

Volume of water left in the tank
= 162000 - 69000
= 93000 cm³

Base area of the tank
= 168000 ÷ 120
= 1400 cm² 

Height of water left in the tank
= 93000 ÷ 1400
≈ 66.4 cm

Answer(s): 66.4 cm