Mirage Company has 30% debt and 70% equity in its capital structure.Its beta is 1.2.The risk-free rate of return is 3% and the market rate of return is 10%.Its tax rate is 40%.It is contemplating whether to increase its debt level to 40% or 50% or keep it at 30%. The table below shows its cost of debt at different capital structure levels.

Debt/Asset Cost of debt, r_d % Beta Cost of equity, r_s % WACC

0.30 current81.2

0.4010

0.5012

Complete the table and state which of the three debt levels is the best. (Hint: first calculate unlevered beta).