Amazon has a beta of $1\mathrm{.}24.$ The yield on $10-$year treasury bonds is $4\mathrm{.}5\%.$ Market Index began the year at $15,500$ and ended the year at $17,650.$ The cost of equity for Amazon is:

a$.$

$14\mathrm{.}55\%$

b$.$

$16\mathrm{.}12\%$

c$.$

$13\mathrm{.}88\%$

d$.$

$17\mathrm{.}95\%$