Manchester Corporation, a U. S. corporation, incurred $100,000 of interest expense during the current year. Manchester manufactures inventory that is sold within the United States and abroad. The total tax book value of its U. S. production assets is $25,000,000. The total tax book value of its foreign production assets is $15,000,000. What amount of interest expense is apportioned to the company's foreign source income for foreign tax credit purposes, assuming the interest expense is fully deductible in the current year