Dana has a portfolio of 8 securities, each with a market value of $5,000. The current beta of the portfolio is 1.28 and the beta of the riskiest security is 1.75. Dana wishes to reduce her portfolio beta to 1.15 by selling the riskiest security and replacing it with another security with a lower beta. What must be the beta of the replacement security? a. 1.21 b. 0.91 c. 0.73 d. 1.62