The common stock of Air United, Inc., had annual returns of 15.6 percent, 2.4 percent, -11.8 percent, and 32.9 percent over the last four years, respectively. What is the standard deviation of these returns? Group of answer choices 13.29 percent 14.14 percent 16.50 percent 17.78 percent 19.05 percent show your work please and let me know if we can solve it by financial calculator