An empty rectangular tank has a capacity of 77 ℓ and a height of 70 cm. At 8 a.m., Tap D is turned on to fill the tank at a rate of 10 ℓ per minute for 20 minutes. After 5 minutes, Tap E is turned on to drain water from the tank at a rate of 8 ℓ per minute for 15 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 
8 ℓ = 8000 cm³ 
77 ℓ = 77000 cm³

Volume of water flowed in from Tap D
= 20 x 10000
= 200000 cm³

Volume of water from drained from Tap E
= 15 x 8000
= 120000 cm³

Volume of water left in the tank
= 200000 - 120000
= 80000 cm³

Base area of the tank
= 77000 ÷ 70
= 1100 cm² 

Height of water left in the tank
= 80000 ÷ 1100
≈ 72.7 cm

Answer(s): 72.7 cm