Use the single-index model to find the market variance and calculate the correlations

Monthly data for GE, IBM, Exxon (XON), and GM: Rm denotes the market return Rf denotes the (nominal) one-month T-Bill rate Monthly data for GE, IBM, Exxon (XON), and GM: Rm denotes the market return Rf denotes the (nominal) one-month T-Bill rate