Is interest paid on each of the debt obligations described below subject to tax under 881(a)? Is it subject to withholding under 1141 or 1142 of the Internal Revenue Code?

a) A New York branch of a Swiss bank makes a loan to a Delaware corporation for use in its U.S. businesses?

b) A Cayman Islands bank makes a loan to a Swiss branch of a Delaware corporation.

c) A Saudi Arabia corporation holds a subordinated debenture issued by a Florida corporation on which interest is paid twice and year and also owns 15 percent of the corporation's stock. The debenture is guaranteed by a Panamanian corporation, which owns 85 percent of the Florida corporation's stock. The Florida corporation directly makes one interest payment during the year and defaults on the other interest payment so that the Panamanian corporation makes the payment as guarantor and receives a fee from the Florida corporation for the guarantee. In addition to addressing the treatment of interest paid, what is the tax treatment of the guarantee fee?

d) A California corporation purchases equipment from an unrelated Brazilian corporation for $50,000. The California corporation pays the invoice for the equipment late, and the terms of purchase require that $500 be paid in addition to the purchase price.