Executive Rule No. 25 establishes the tax treatment for supplies, particularly imported materials and equipment. It stipulates maximum allowable cost percentages based on the supplier's relationship with the importing body: 85% for Head Office, 90% for related companies, and 95% for unrelated companies. The rule details the components of supply costs, such as CIF/FOB value and customs duties, and provides a formula to determine revenues if unspecified. It also addresses exemptions under double taxation agreements, the handling of local purchases, and procedures for exceptional cases.