An outstanding issue of Public Express Airlines debentures has a call provision attached. The total principal value of the bonds is $280 million, and the bonds have an annual coupon rate of 13 percent. The company is considering refunding the bond issue. Refunding means that the company would issue new bonds and use the proceeds from the new bond issuance to repurchase the outstanding bonds. The total cost of refunding would be 14 percent of the principal amount raised. The appropriate tax rate for the company is 35 percent.

How low does the borrowing cost need to drop to justify refunding with a new bond issue?