4. Using monthly data available on Yahoo! Finance, calculate the historical betas of Apple Inc. and The Kellogg Company for the 5-year period ending January 1, 2021. [Note: as a shortcut, you may assume one month U.S. T-bills yielded 0% throughout the period from 1/1/16 to 1/1/21. Using actual T-Bill returns to calculate the monthly excess returns of these securities and the S&P 500 Index should not materially alter the results of these calculations.]