Please show me how to find the answer in Microsoft Excel. I need to know the formula/inputs used in the solution.

The correlation between the returns of three stocks A, B, C are given in the following tables: The expected rates of returns on A,B, and C are 16%,12%, and 15% respectively. The corresponding standard deviations of the returns are 25%,22%, and 25%. a. What is the standard deviation of a portfolio invested 25% in stock A, 25\% in stock B, and 50% in Stock C? (17.80%) b. You plan to invest 50% of your money in the portfolio constructed the part a and 50% in the risk-free assets. The risk-free interest rate is 5%. What is the expected return on this investment? What is the standard deviation of the returns on this investment? (9.75%,8.9%)