You want to invest in Apple, Inc. stock and would like to consider the risk of the company. You found that Apple's annual returns for the last five years were -6%, 55%, 38.71%, -8.396, and 121.7396. Calculate the standard deviation using this sample of Apple's returns. (Hint: you first need to find the average return) O a. 38.71% O b.53.2896 O c. 66.05% O d. 40.23%