What quantity of water should taken out to concentrate 21 liters of 40% acidic liquid to 60% acidic liquid?	Choose the correct answer.
A) 5liters B) 10liters C) 7liters D) 8liters E) 6liters
Required answer is = 21(60-40)/60 = 7 liters   Answer is 7liters
<result>C</result>
What quantity of water should taken out to concentrate 21 liters of 40% acidic liquid to 60% acidic liquid?