Question: The St. Louis, San Francisco and Texas Railway (SLSF), was a subsidiary railway to the St. Louis-San Francisco Railway, in 1980 it merged into which United States-based railroad company formed from a merger of four major U.S. railroads?
Sentence (from "St. Louis, San Francisco and Texas Railway"): The Frisco, including the subsidiary, formed a large X-shaped system across the states of Kansas, Missouri, Oklahoma, Texas, Arkansas, Mississippi and Alabama.
Relevant evidence: No