Suppose you purchase a set of furniture worth $$6000$ with simple interest of $\%1\mathrm{.}5$ per months. You plan to finance the furniture for $4$ years. The seller's administration fee for processing the add$-$on loan is $$225$ that they add it to the loan amount. a$)$ what is your monthly payment? b$)$ What is the annual effective interest rate you are paying?