Suppose that Fabulous had purchased trucks for $400,000 which were used solely in the transportation of inventory purchased in different parts of the United States to U.S customers. All transportation expenses, including depreciation deductions of $200,000 in respect of the trucks were applied to reduce U.S-source income. Fabulous than results the used trucks for $410,000, thereby realizing income of $210,000 to a foreign purchaser that took title to the trucks in Peru. What is the source of the income realized on the sale of the trucks?