Suppose you held a well-diversified portfolio with a very large number of securities, and that the single index model holds.

Suppose you held a well-diversified portfolio with a very large number of securities, and that the single index model holds. If the standard deviation of your portfolio was 42% and the standard deviation of the market was 18%, what would be your estimate of the beta of the portfolio?  Hint:  Note that a well-diversified portfolio will have a firm-specific variance and a residual standard deviation = 0%.