i need help getting the standard deviation of the portfolios with each stock and which one should i add?

You have a portfolio with a standard deviation of 29% and an expected return of 18%. You are considering adGing one of tee two stocks in the following bable If after adding the stock you wit have 20\% of your money in the new stock and 80% of your money in your existing portlolio, which one should you add? Standard deviation of the portiolio with stock A is 4. (Round to two decimal places.)