Armadillo Mfg. Co. has a target capital structure of 50% debt and 50% equity. They are planning to invest in a project which will necessitate raising new capital. New debt will be issued at a before-tax yield of 12%, with a coupon rate of 10%. The equity will be provided by internally generated funds. No new outside equity will be issued. If the required rate of return on the firm's stock is 15% and its marginal tax rate is 40%, compute the firm's cost of capital.

a.11.1%
b.7.2%
c.13.5%
d.12.5%