Algebra 2 (1st Edition)

He invested $8500$ in $5\%$ and $6500$ in $7\%$ interest bonds.
Let $x$ be the amount he invested in $5\%$ interest bonds. Then the amount he invested in $7\%$ interest bonds is $15000-x$. Then our equation is: $0.05x+(15000-x)0.07=880\\0.05x+1050-0.07x=880\\-0.02x=-170\\x=8500$ Thus he invested $8500$ in $5\%$ and $6500$ in $7\%$ interest bonds.