Please show work without using excel

You want to create a $80,000 portfolio comprised of two stocks plus a risk-free security. Stock A has an expected return of 15 percent and Stock B has an expected return of 17 percent. You want to own $30,000 of Stock B. The risk-free rate is 5 percent and the expected return on the market is 12 percent. If you want the portfolio to have an expected return equal to that of the market, how much should you invest in the risk-free security?