Question 1) Peter has a $ 4 million portfolio consisting of a $400,000 investment in each of 10 different stocks. The portfolio has a beta of 1.4. Peter is considering selling $400,000 worth on one stock with a beta of 1.5 and using the proceeds to buy another stock with a beta of 0.85. What will the portfolios new beta be after these transactions?

I'm assuming you can use the Capital Asset Pricing Model formula on this question but I am unsure. Any help is much appreciated!