By selling an article for $90, a person gains $15. What is the gain %? Choose the correct choice from the following answers.
A) 25 %  B) 30 %  C) 50 %  D) 20 %  E) 10 %

Rationale: "s . p . = $ 90 gain = $ 15 c . p . = 90 - 15 = 75 gain % = 15 / 75 * 100 = 20 % answer is d"
Answer: D