Task: Question Answering
Input (English): Problem: a chemical supply company has 60 liters of a 35 % hno 3 solution. how many liters of pure undiluted hno 3 must the chemists add so that the resultant solution is a 50 % solution ?
Options: a. 18, b. 15, c. 20, d. 24, e. 30
Output (English): a