You have an outstanding student loan with required payments of $$$$600$ per month for the next $4$ years. The interest rate on the loan is $8\mathrm{.}50\%$ APR$($monthly$).$ You are considering making an extra payment of $$$$200$ today$($i$.$e$.,$ you will pay an extra $$$$200$ that you are not required to$$ pay$).$ If you are required to continue to make payments of $$$$600$ per month until the loan is paid$$ off, what is the amount of your final$$ payment? What effective rate of return$($expressed as an APR with monthly$$ compounding$)$ have you earned on the $$$$200?($Note$$: Be careful not to round any intermediate steps less than six decimal$$ places.$)$