"Find the standard deviation of monthly stock returns for Spider Web Inc. if its most recent monthly stock returns were $6\%,-15\%,$ and $6\%.$ Use the population standard deviation formula."

$9\mathrm{.}90\%$

$8\mathrm{.}46\%$

$7\mathrm{.}77\%$

$12\mathrm{.}57\%$

$6\mathrm{.}79\%$