need the formulas

You've observed the following returns on Crash-n-Burn Computer's stock over the past five years: 7 percent, -13 percent, 21 percent, 34 percent, and 15 percent. What was the arithmetic average return on the stock over this five-year period? What was the variance of the returns over this period? The standard deviation? Complete the following analysis. Do not hard code values in your calculations. Deviation Squared Deviation Year 1 2 3 4 5 Actual Return 0.07 (0.13) 0.21 0.34 0.15 Sum = = Squared deviation total Average return = Variance =