Molly deposits $X at the end of each month with the first deposit occurring one month from now and the last payment occurring after $20$ years. The savings account pays an annual effective interest rate of $6\mathrm{.}9\%\mathrm{.}25$ years from now, Molly would like to buy an annuity that will pay $$20,000$ annually for $15$ years, with the first payment occurring one year after the purchase and annual rate of $1\mathrm{.}5\%.$Calculate monthly savings, X$.$the answer is $381$ and i need step by step