Seduak Has Estimated the Costs of Debt and Equity Capital

Seduak has estimated the costs of debt and equity capital for various proportions of debt in its capital structure: $\begin{array}{rrr}\% \text { of Debt } & \text { Cost of Debt }(\%) &\text { Cost of Equity }(\%) \\0 & - & 13.0 \\10 & 5.4 & 13.3 \\20 & 5.4 & 13.8 \\30 & 5.8 & 14.4 \\40 & 6.3 & 15.2 \\50 & 7.0 & 16.0 \\60 & 8.2 & 17.0\end{array}$
Based on these estimates, determine Seduak's optimal capital structure.

A) 30% debt
B) 40% debt
C) 50% debt
D) 60% debt