Complex sentence: The 1973-S was struck for inclusion in base-metal proof sets, as well as the regular "blue Ikes" and "brown Ikes" though sales of the part-silver pieces dipped to a total of just under 2.9 million.
Split into simpler sentences: The 1973-S was struck for inclusion in base-metal proof sets, as well as the regular "blue Ikes" and "brown Ikes". Sales of the part-silver pieces dipped to a total of just under 2.9 million.