Please solve by hand

Consider the following two assets: Asset Expected Return Standard Deviation S&P 500 ETF (U.S. Stocks) 8.0% 18% Treasury Bills 1.0% 0% A. What are the expected return and standard deviation of a portfolio that is 90% invested in the S&P 500 ETF and 10% invested in Treasury Bills? B. Say you want to form a portfolio that has a standard deviation of 12%. How much of your portfolio do you need to invest in the S&P 500 ETF and in Treasury Bills? C. You are eager for a higher return and want a portfolio with an expected return of 16.75%. How much of your portfolio do you need to invest in the S&P 500 ETF and in Treasury Bills? D. How would you interpret the magnitude and signs of the weights in Part C