a) In return for payments of $200 at the end of 5 years and $300 at the end of 10 years, a man agrees to pay X at the end of 3 years and 2X at the end of 6 years. Determine X if d = 3 ½%.

b) The present value of two payments of $100 each to be made at the end of n years and 2n years is $100. If i = .035, determine n.