pamela borrowed $$15,000$ for an ivestment purpose on march $12$ on a demand note for a variable rate of interest and payment of any accrued interest on december $31.$she repaid $$1500$ on june $17,$ $$1850$ on september $10,$ and $$3000$ on november $8.$ how much is the final payment on december $31$ if the rate of interest was $12\mathrm{.}5\%$ on march $12,9\mathrm{.}75\%$ effective august $1,$ and $7\mathrm{.}45\%$ effective october $1?$use the declining balance approach