Based on the following information, what is the firm's weighted average cost of capital of the operating assets, WACC $C_0?$

Cost of debt, $R_D$:$7\%$

Cost of equity, $R_S$:$20\%$

Total market value of debt, D: $500$

Total market value of equity, $S$:$1,500$

Number of common shares outstanding: $100$

Total market value of non$-$operating assets, N: $200$

Cost of non$-$operating assets, $R_N$:$9\%$

Corporate tax rate, T: $40\%$

a$.\mathrm{.}168751$

b$.\mathrm{.}188232$

c$.\mathrm{.}143009$

d$.\mathrm{.}127767$