I sold a book at a profit of 12%. Had I sold it for $18 more, 18% would have been gained. Find the cost price? Choose the correct option
A) $ 100 B) $ 250 C) $ 300 D) $ 200 E) $ 180

Rationale: "118 % of cost - 112 % of cost = $ 18 6 % of cost = $ 18 cost = 18 * 100 / 6 = $ 300 answer is c"
Answer: C