A 40-liter solution of alcohol and water is 5 percent alcohol. If 2.5 liters of alcohol and 7.5 liters of water are added to this solution, what percent of the solution produced is alcohol?
Choose the correct answer.
A) 9 %  B) 12 %  C) 15 %  D) 18 %  E) 21 %

Rationale: "the percent of alcohol in the solution is ( 0.05 ( 40 ) + 2.5 ) / 50 = 4.5 / 50 = 9 % the answer is a ."
Answer: A