For the period of $2002$ to $2007,$ rhe rrturns to the S&P $500$ index were: $-23\mathrm{.}4\%,26\mathrm{.}4\%,9\mathrm{.}0\%,3\mathrm{.}0\%,13\mathrm{.}6\%,3\mathrm{.}5\%$ compute the arithmetic average annual return for the S&P $500$ index for this time period