O'Brien Inc. has the following data: rRF $=5\mathrm{.}00\%$; RPM $=7\mathrm{.}00\%$; and b $=1\mathrm{.}55.$ What is the firm's cost of equity from retained earnings based on the CAPM?

a$.14\mathrm{.}75\%$

b$.18\mathrm{.}60\%$

c$.13\mathrm{.}55\%$

d$.15\mathrm{.}85\%$

e$.12\mathrm{.}00\%$