Table of stock returns of three companies: Stock Returns Year North Air West Air Tex Oil 2013 21% 9% -2% 2014 30% 21% 5% 2015 7% 7% 9% 2016 -5% -2% 21% 2017 -2% -5% 30% 2018 9% 30% 7% a. Calculate average return and standard deviation of each stock. b. Portfolio NW has 50% capital invested in North Air and 50% capital invested in West Air. Portfolio WT has 50% capital invested in West Air and 50% capital invested in Tex Oil. Calculate average return of each portfolio. Without calculation, which portfolio has lower risk and why