Formulate but do not solve the problem. kelly fisher invested a total of $20,000 in two municipal bonds that have yields of 8% and 9% interest per year, respectively. if the interest kelly receives from the bonds in a year is $1680, how much did she invest in each bond? (let x and y denote the amount, in dollars, invested at 8% and 9%, respectively.)
= 20,000 = 1680