Milhouse's father gets a new job, and increases his offer to $$800$ at the end of each month for four years, or he will give him $$35,000$ right now. Assume an annual interest rate of $7\mathrm{.}5\%.$ What would the annual interest rate need to be for Milhouse to be indifferent about accepting either option? $($do not enter the $\%$ sign in the answer box$)$