I know the answer, but how do I get the answer? Please explain so I know how to do work these types of problems.

Sharon Stonewall currently has an investment portfolio that contains 10 stocks that have a total value equal to $160,000. The portfolio has a beta equal to 1.0. Sharon wants to invest an additional $40,000 in a stock with beta = 2.0. After Sharon adds the new stock to her portfolio, what will be the portfolio's beta? A. 1.2 B. 1.5 C. 2.0 D. Not enough information is given to compute the portfolio's beta E. None of the above is correct