求助： 学过investment 的人进！

求作业题 和考试卷子。。谢啦。。。
或者帮我做一下这份作业 谢啦！！
Tripco shares are selling at $90 per share. An investor sells 4000 shares short. The initial margin requirement is 30% and maintenance margin is 20%. Brokerage fees are $50 plus $0.025 per share per trade. The investor closes out the short position after 45 days when the shares are selling at $91.50 per share. While the investor is in the short position, the company declares and pays dividends of $1.25 per share.
What is the annualized rate of return to the investor?
At what price will there be a margin call?


a. Suppose you bought a $1000 face value, 20-year, zero-coupon bond with yield to maturity of 9%. After 2 years, the yield to maturity on the bond is 7.5% and you sell the bond. What is your annual realized yield? (Assume semi-annual coupon payments on similar bonds with coupon payments).
b. An investor buys a $1,000 face value bond with 3 years to maturity. The yield to maturity of the bond is 10% and the coupon rate is 9%, what is the (Macauley) duration of this bond, assuming semi-annual coupon payments.

c. Suppose you have $100,000 to invest in a portfolio made up of the bond in (b) above and another bond with duration of 4.2 years. Your investment horizon is 3 years. How will you allocate the funds between the two bonds in order that your portfolio will be immunized?