A person borrows Rs. 4000 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 choices:
A) 100 rs  B) 80 rs  C) 160 rs  D) 180 rs  E) 200 rs

Rationale: "gain in 2 years = [ ( 4000 * 6 * 2 ) / 100 ] - [ ( 4000 * 4 * 2 ) / 100 ] 480 - 320 = 160 gain in 1 year = ( 160 / 2 ) = 80 rs answer : b"
Answer: B