BunCo, a U.S. corporation, owns a number of patents related to designing sunglasses. BunCo licenses these patents to unrelated parties. SpainCo, a Spanish corporation, paid BunCo $78,000 in royalties related to these licenses. SpainCo uses the patent information in its manufacturing process in its Texas plant. WiscCo, a U.S. corporation, paid BunCo $32,000 in royalties related to the licenses. WiscCo uses the patent information in its manufacturing process in its Germany manufacturing plant. How much U.S.-source royalty income did BunCo earn from these licenses?

a.$32,000

b.$0

c.$110,000

d.$78,000