Your firm is considering the purchase of a new bus to replace the one they have in use, which cost $ 17,000 five years ago. The old bus has operational and maintenance costs $ 1,200 per year and can last up to five years with no re-sale value. However, if it were sold today are people willing to pay $ 5,000 for it. The new bus will cost $ 27,000 and a market value of $ 8000 in five years. It expects its operating and maintenance costs alone are $ 600 a year. Use a MARR of 20% and a period of study of five years to determine whether to replace the old bus. Identify the "defend" and "challenger" with their flow charts.