you have just received a windfall from an investment you made in a friend's business. she will be paying you $$30,000$ at the end of this year, $$60,000$ at the end of next year, and $$90,000$ at the end of the year after that $(3$ years from today$)$ the interest rate is $7\mathrm{.}5\%$ per year. what is the present value of your windfall?