A couple will retire in $50$ years; they plan to spend about $$28,000$ a year $($in current dollars$)$ in retirement, which should last about $25$ years. They believe that they can earn a real interest rate of $8\%$ on retirement savings.

a$.$ If they make annual payments into a savings plan, how much will they need to save each year? Assume the first payment comes in $1$ year.

b$.$ How would the answer to part $($a$)$ change if the couple also realize that in $20$ years they will need to spend $$58,000$ on their child$$s college education?