An empty rectangular tank has a capacity of 70 ℓ and a height of 20 cm. At 7 a.m., Tap P is turned on to fill the tank at a rate of 8 ℓ per minute for 16 minutes. After 12 minutes, Tap Q is turned on to drain water from the tank at a rate of 4 ℓ per minute for 5 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 
4 ℓ = 4000 cm³ 
70 ℓ = 70000 cm³

Volume of water flowed in from Tap P
= 16 x 8000
= 128000 cm³

Volume of water from drained from Tap Q
= 5 x 4000
= 20000 cm³

Volume of water left in the tank
= 128000 - 20000
= 108000 cm³

Base area of the tank
= 70000 ÷ 20
= 3500 cm² 

Height of water left in the tank
= 108000 ÷ 3500
≈ 30.9 cm

Answer(s): 30.9 cm