Present value $($with changing interest rates$).$ Marty has been offered an injury settlement of $$12,000$ payable in $4$ years. He wants to know what the present value of the injury settlement is if his opportunity cost is $3\mathrm{.}5\%.($The opportunity cost is the interest rate in this problem.$)$ What if the opportunity cost is $6\mathrm{.}5\%?$ What if it is $11\mathrm{.}5\%?$