Core Concepts Inc,. has experienced stock returns of $8\mathrm{.}4\%,6\mathrm{.}3\%,$ and $14\mathrm{.}2\%$ over the last three years. Over this time period, what has been the firm's arithmetic average annual rate of return?

Question $8$Select one:

a$.$

$9\mathrm{.}58\%$

b$.$

$9\mathrm{.}63\%$

c$.$

$9\mathrm{.}88\%$

d$.$

$9\mathrm{.}92\%$