Can someone teach me how to find standard deviation?

Homework: Homework 4 Question 6, P7-7 (similar to) Part 2 of 5 HW Score: 65.44%, 4.58 of 7 points Points: 0.2 of 1 Save (Expected rate of return and risk) Syntex, Inc. is considering an investment in one of two common stocks. Given the information that follows, which investment is better, based on the risk (as measured by the standard deviation) and return? Common Stock A Common Stock B Probability Return Probability Return 0.25 10% 0.15 -4% 0.50 14% 0.35 5% 0.25 18% 0.35 15% 0.15 20% (Click on the icon in order to copy its contents into a spreadsheet.) a. Given the information in the table, the expected rate of return for stock Ais 14.00 %. (Round to two decimal places.) The standard deviation of stock Ais %. (Round to two decimal places.)