An investor has mean-variance preferences given by Up 0) = 4,-9. where Wp is the expected return on the investor's portfolio, o, is the variance of the investor's portfolio, and p > O is a parameter describing the investor's risk aversion. Suppose all investments available to the investor are located on the security market line which cuts through the risk-free return = 3% and the market portfolio with expected return r = 7%. The variance of the market portfolio is 16% Derive the critical value of p such that the optimal portfolio weight on the risk-free asset is 80%