12.6 portfolio (.4 x 6)+(.6 X 13) = 10.2%. This portfolio's beta is .6, since $600,000, which is 60% of the investment, is in the market portfolio. Investors in a stock with a beta of .6 would not buy it unless it also offered a rate of return of 10.2% and would rush to buy if it offered more. The stock price would adjust until the stock's expected rate of return was 10.2%.