4. (10 points) The following table gives current prices of U.S. Treasury bonds: Half the stated coupon is assumed to be paid every six months. (a) Calculate the implied zero spot rates (p.a. and continuously compounded) for maturities of 6 months, 12 months, 18 months, and 24 months. (b) Suppose you can borrow and lend $100 at the zero spot rates computed in (a). Today, someone is offering you to invest money in USD at 4% (p.a. and continuously compounded) for a 6 month period starting in 18 months. Is there an arbitrage opportunity? If yes, explain carefully how the arbitrage strategy looks like and what the arbitrage gain in 24 months would be