could you go in depth with b part ?

4. A money marager is holding the following portfolio. Stock: Amount Invested: Beta: $300.000 $400,000 $500,000 600,000 0.6 1.05 1.25 1.8 a) What is the beta of the portfolio? b) If the marager would like to sell all of her holdings of stock I for $300.000 and use the proceeds to purchase $300,000 more of stock 4 if the risk free rate is 6% and the original portfolio's required return is 12%, what would be the new portfolio's required return