Glen Campbell owns a small office building adjacent to an airport. He acquired the property $10$ years ago at a total cost of $$608,000-$that is$,$ $$70,000$ for the land and $$538,000$ for the building. He has just received an offer from a realty company that wants to purchase the property; however, the property has been a good source of income over the years, and so Campbell is unsure whether he should keep it or sell it$.$ His alternatives are as follows:

a$.$ Keep the property. Campbell's accountant has kept careful records of the income realized from the property over the past $10$ years. These records indicate the following annual revenues and expenses: Campbell makes a $$13,450$ mortgage payment each year on the property. The mortgage will be paid off in eight more years. He has been depreciating the building by the straight$-$line method, assuming a salvage value of $$80,700$ for the building, which he still thinks is an appropriate figure. He feels sure that the building can be rented for another $15$ years. He also feels sure that $15$ years from now the land will be worth three times what he paid for it$.$

$\backslash$table$[[$Rental receipts,,$$160,000$