Now you have $1,000,000 to invest. If you invest $195,000 in stock A (expected return rate is 195000/1000000, beta is 0.32), and invest $340,000 in stock B (expected return rate is 340000/1000000, beta is 0.8). Then you invest $135,000 in risk-free asset (risk free rate is not given, you need to calculate) and invest the rest money in stock C. Whats the beta of stock C? You can regard investment value as expected value here.