I need help with this question

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 10 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.

Ten stocks Ebay, Starbuck, Facebook, Twitter, Samsung, Netflix, Johnson and Johnson, Centene Corporation, Apple. Data can be obtained through the finance.yahoo.com

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