Returns for the Shields Company over the last three years are shown below. What's the standard deviation of Shields' returns? (Hint: This is a sample, not a complete population, so the sample standard deviation formula should be used.) Year Return 2009 21.50% 2008 -12.50% 2007 24.20% 19.94% 20.45% Ob Oc. 20.97% Od 21.49%