I need help with this question and everything I copied through the book, there is no any more relevant information

You can download data for the following questions from finance.yahoo.com.Use the Beyond the Page feature to access an Excel program for calculating the efficient frontier.(We are grateful to Darien Huang for providing us with a copy of this program.) Excel functions SLOPE, STDEV, COVAR, and CORREL are especially useful for answering the followingquestions.

a. Download up to 10 years of monthly returns for 4 different stocks and enter them intothe Excel program. Enter some plausible figures for the expected return on each stock andfind the set of efficient portfolios. Assume that you cannot borrow or lend. Any 5 stocks can be found through the finance.yahoo.com

Facebook, Amazon, Tesla, Netfli are my 4 stocks, date 10 years from Nov 12, 2009 to Nov 12, 2019 in 10 years

Facebook data:https://finance.yahoo.com/quote/FB/history?period1=1258012800&period2=1573545600&interval=1mo&filter=history&frequency=1mo ( and choose download)

Amazon data: https://finance.yahoo.com/quote/AMZN/history?p=AMZN&.tsrc=fin-srch

Tesla https://finance.yahoo.com/quote/TSLA/history?period1=1258012800&period2=1573545600&interval=1mo&filter=history&frequency=1mo

Netflix data: https://finance.yahoo.com/quote/NFLX/history?p=NFLX&.tsrc=fin-srch

b. How does the possibility of short sales improve the choices open to the investor?