Suppose a stock has generated the following annual returns: $13\mathrm{.}2\%,-11\mathrm{.}4\%$ and $7\mathrm{.}2\%.$ What was the standard deviation of its returns? Answer in percent, rounded to two decimal places $($e$.$g$.,4\mathrm{.}32\%=4\mathrm{.}32).$