If 20 liters of chemical X are added to 80 liters of a mixture that is 20% chemical X and 80% chemical Y, then what percentage of the resulting mixture is chemical X?  Select the correct option:
A) 30 %
B) 33 %
C) 36 %
D) 39 %
E) 42 %

Rationale: "the amount of chemical x in the solution is 20 + 0.2 ( 80 ) = 36 liters . 36 liters / 100 liters = 36 % the answer is c ."
Answer: C