By selling 90 pens, a trader gains the cost of 15 pens. Find his gain percentage?
Choose the correct choice from the following answers:	A) 16.66 %	B) 17.66 %	C) 18.66 %	D) 19.66 %	E) 20.66 %

Rationale: "let the cp of each pen be rs . 1 . cp of 90 pens = rs . 90 profit = cost of 15 pens = rs . 15 profit % = 15 / 90 * 100 = 16.66 % answer : a"
Answer: A