Question: Westmoreland County, Pennsylvania is located west of a mountain range that runs for about how many miles?

Context paragraphs:
New Kensington–Arnold School District: The New Kensington–Arnold School District is a small, suburban, public school district serving the cities of Arnold and New Kensington, located in northern Westmoreland County in the U.S. state of Pennsylvania.  The New Kensington–Arnold School District encompasses approximately 5 sqmi .  According to 2000 federal census data, it served a resident population of 20,400.  By 2010, the District's population declined to 18,265 people.  In 2009, the District residents’ per capita income was $16,285, while the median family income was $36,720.  In Westmoreland County, the median household income was $50,736.  In the Commonwealth, the median family income was $49,501 and the United States median family income was $49,445, in 2010.  The educational attainment levels for the New Kensington-Arnold School District population (25 years old and over) were 89.4% high school graduates and 15.4% college graduates.  The District is one 17 public school districts in Westmoreland County and one of the 500 public school districts of Pennsylvania.

Pennsylvania Route 981: Pennsylvania Route 981 (PA 981) is a state highway which runs 50.4 mi across Westmoreland County, in southwestern Pennsylvania.  The highway begins at Pennsylvania Route 51 in Rostraver Township, Pennsylvania, and runs northward across Westmoreland County, passing through the towns of Mount Pleasant, Latrobe, and New Alexandria before ending at Pennsylvania Route 819 in Salina.

Yough Senior High School: Yough Senior High School is a high school located in the southeastern region of Westmoreland County, Pennsylvania, USA (Parents of Students/Staff/Educators).  The school is operated by the Yough School District.  Students attend from the townships of Sewickley Township, Westmoreland County, Pennsylvania and South Huntingdon.  Yough High School has graduating class sizes from 180-200.

Rostraver Airport: Rostraver Airport (ICAO: KFWQ) is a public use airport in Westmoreland County, Pennsylvania, United States.  It is located five nautical miles (9 km) east of the central business district of Monongahela, Pennsylvania in Rostraver Township.  It is operated by the Westmoreland County Airport Authority, which also operates the Arnold Palmer Regional Airport in Unity Township, Pennsylvania.

Penn-Trafford High School: Penn-Trafford High School is a public high school located in Harrison City, Pennsylvania in Westmoreland County, and is the secondary school serving the Penn-Trafford School District.  It is the result of several mergers of smaller school districts and entities.  It is the successor of Penn Joint High School and Trafford High School.  The school colors are green and gold.  The different government entities that are incorporated into this school district are, in size order, Penn Township, Trafford Borough, Manor Borough (part), and Penn Borough.  The school district is mainly in Westmoreland County, Pennsylvania with a small part of Trafford Borough in Allegheny County, Pennsylvania.

Trafford, Pennsylvania: Trafford is a borough in Allegheny and Westmoreland counties in the U.S. state of Pennsylvania.  Located near Pittsburgh in western Pennsylvania, the borough lies primarily in Westmoreland County; only a small portion extends into Allegheny County.  It was incorporated in 1904 from the northernmost corner of North Huntingdon Township, and was named by George Westinghouse for Trafford near Manchester, England.  The population was 3,174 at the 2010 census.  Of this, 3,113 were in Westmoreland County, and only 61 were in Allegheny County.

Arnold Palmer Regional Airport: Arnold Palmer Regional Airport (IATA: KLBE, ICAO: LBE) is a public airport in the eastern United States, located in Westmoreland County, Pennsylvania, two miles (3 km) southwest of Latrobe and about 33 mi southeast of Pittsburgh.  It is owned by the Westmoreland County Airport Authority and was formerly "Westmoreland County Airport."

Westmoreland County, Pennsylvania: Westmoreland County is a county located in the U.S. state of Pennsylvania.  At the 2010 census, the population was 365,169.  The county seat is Greensburg.  Cut from Lancaster, Northumberland, and later Bedford Counties, Westmoreland County was founded on February 26, 1773 and was the first county in the colony of Pennsylvania in which its entire territorial boundary was located west of the Allegheny Mountains.  Westmoreland County originally included the present-day counties of Fayette, Washington, Greene, and parts of Beaver, Allegheny, Indiana, and Armstrong counties.  It is named for Westmorland, a historic county of England.

Allegheny Mountains: The Allegheny Mountain Range , informally the Alleghenies and also spelled Alleghany and Allegany, is part of the vast Appalachian Mountain Range of the eastern United States and Canada and posed a significant barrier to land travel in less technologically advanced eras.  The barrier range has a northeast–southwest orientation and runs for about 400 miles (640 km) from north-central Pennsylvania, through western Maryland and eastern West Virginia, to southwestern Virginia.

Five Star Trail: The Five Star Trail runs nearly 8 miles through Westmoreland County, in the U.S. state of Pennsylvania.  The trail is alongside an active railroad track, Southwestern Pennsylvania Railroad, that stretches between Lynch Field, a Greensburg city park and Youngwood.  The trail then spurs off eastward to connect with the campus of Westmoreland County Community College and continues on to Armbrust.

Supporting paragraphs: Westmoreland County, Pennsylvania Allegheny Mountains
Answer: 400