Detailed Instructions: In this task, you're given a question, along with a context passage which has extra information available on certain terms mentioned in it. Your job is to determine which sentence(s) from the passage can be used to search for further information needed to answer the question.
Problem:Question: How many years had Fort Pitt existed when Tannehill was assigned there? Passage:Tannehill served in the Continental Army during the American Revolutionary War, initially as the first sergeant in Capt. Thomas Price's Independent Rifle Company, one of the original ten independent companies of riflemen from the frontier regions of Pennsylvania, Maryland, and Virginia authorized by the Continental Congress on June 14, 1775. He received his commission dated January 1, 1776, as a third lieutenant while serving at the Siege of Boston. In June 1776 Tannehill and his company were incorporated into the newly organized Maryland and Virginia Rifle Regiment, at which time he advanced to second lieutenant. Later that year a large portion of his regiment was captured or killed at the Battle of Fort Washington on northern Manhattan Island. However, those members of the unit not taken in the battle, including Tannehill, continued to serve actively with Washington's Main Army, participating in the Battles of Trenton and Princeton, and in the spring of 1777 were administratively attached to the 11th Virginia Regiment. Tannehill was promoted to first lieutenant on May 18, 1777, and the following month he was attached to the newly organized Provisional Rifle Corps commanded by Col. Daniel Morgan, which played a major role in the Battles of Saratoga and a peripheral role in the Battle of Monmouth. He returned to the Maryland and Virginia Rifle Regiment (his permanent unit) in mid-1778 when Lt. Col. Moses Rawlings, the regiment's commander who had been exchanged from British captivity earlier that year, was marshaling the remnants of his unit and recruiting new members while stationed at Fort Frederick, Maryland. In early 1779 Tannehill and the regiment were assigned to Fort Pitt of present-day western Pennsylvania where they supplemented other Continental forces engaged in the defense of frontier settlements from Indian raids. Tannehill advanced to the rank of captain on July 29, 1779, and he commanded the regiment in late 1780. He was discharged from service on January 1, 1781, when his unit was disbanded.

Solution:
In early 1779 Tannehill and the regiment were assigned to Fort Pitt of present-day western Pennsylvania where they supplemented other Continental forces engaged in the defense of frontier settlements from Indian raids