I sold a book at a profit of 10%. Had I sold it for $140 more, 15% would have been gained. Find the cost price? Select the correct option: A) $ 2000 B) $ 2500 C) $ 3000 D) $ 2800 E) $ 1540

Rationale: "115 % of cost - 110 % of cost = $ 140 5 % of cost = $ 140 cost = 140 * 100 / 5 = $ 2800 answer is d"
Answer: D