john invested $4000 into stocks(s) and bonds(b). The stocks earned 7% interest. the bonds earned 9% interest. if the investment earned $300, how much money did john have in stocks and bonds. my question- how do I write this formula so I can find the answer

Answer 1

4000=S+ B

300=0.07S + 0.09B

to solve, B=4000-S or
300=0.07S + 0.09(4000-S) then solve for S