The Martian Corporation, a space vehicle development company, is starting a new division that will develop the next$-$generation launch missile engine configuration. Use a hand application of the MIRR method to determine the EROR for the estimated net cash flows $($in $$1000$ units$)$ of $$-44,000$ in year $0,$ $$15,000$ in years $1$ through $6\mathrm{.}00,$ and $$-8,000$ in year $7\mathrm{.}00.$ Assume a borrowing rate of $8\mathrm{.}00\%$ and an investment rate of $21\mathrm{.}00\%$ per year. $($Round the final answer to three decimal places.$)$

The external rate of return is $?\%$