A person borrows Rs. 9000 for 2 years at 4% p.a. simple interest. He immediately lends it to another person at 6 p.a for 2 years. Find his gain in the transaction per year.  Choose the correct choice from the following:	A) 100 rs	B) 150 rs	C) 160 rs	D) 180 rs	E) 200 rs

Rationale: "gain in 2 years = [ ( 9000 * 6 * 2 ) / 100 ] - [ ( 9000 * 4 * 2 ) / 100 ] 1080 - 720 = 360 gain in 1 year = ( 360 / 2 ) = 180 rs answer : d"
Answer: D