Please help with this question, thank you!

Using the data in the following table, and the fact that the correlation of A and B is 0.72, calculate the volatility (standard deviation) of a portfolio that is 50% invested in stock A and 50% invested in stock B. (Click on the following icon o. in order to copy its contents into a spreadsheet.) Year 2008 2009 2010 2011 2012 2013 Realized Returns Stock A Stock B - 1% 13% 15% 38% 9% 12% - 10% - 1% 3% -9% 8% 27% The standard deviation of the portfolio is %. (Round to two decimal places.)