D'Anconia Copper is considering issuing a one-year debt, and has come up with the following estimates of the value of the interest tax shield and the probability of distress for different levels of debt: If, in the event of distress, the present value of distress costs is equal to $10 million, then the optimal level of debt for D'Anconia Copper is: $0 $25 millions $50 millions $60 millions $70 millions $80 millions $90 millions