Complex sentence: The company had built television stations KTLA in Los Angeles and WBKB in Chicago, and invested US $400,000 in the DuMont Television Network, which operated stations WABD, WTTG, and WDTV in New York City, Washington, D.C., and Pittsburgh.
Split into simpler sentences: The company had built television stations KTLA in Los Angeles and WBKB in Chicago. It had also invested US $400,000 in the DuMont Television Network, which operated stations WABD, WTTG, and WDTV in New York City, Washington, D.C., and Pittsburgh.