Need help with question 12, 13, 14. thank you

IV. Duration Using Excel, calculate the duration of the following bonds. Assume all have a face value of $100 and a 7% yield to maturity. 10. A 5-year zero coupon note: (a) 7 years; (b) 4.2 years; (c) 5 years; (d) 0 years; 11. A 7-year bond with coupon of 4.0%: (a) 4.57 years; (b) 532 years; (c) 0 years; (d) 6.16 years; 12. A 10-year bond with coupon of 9.0%: (a) 10 years (b) 7.2 years; (c) 0 years; (d) 5.9 years; Assume you hold a bond portfolio with an average yield to maturity of 5% and a duration of 5 years 13. What would be the effect of a 100 basis point reduction in yields on the value of the bond portfolio: (a) +5.0%; (b)-100%; (c) +4.76%; (d) -5.0%; 14. What new yield to maturity would make the portfolio lose half its value: (a) 5.5%; (b) 15.5%; (c) 4%; (d) 50%