You will be given a definition of a task first, then some input of the task.
In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: In 1968, Texas head coach Darrell Royal and his offensive coordinator Emory Bellard introduced what would become known as the wishbone offense. The wishbone was derived from the Split-T offense run at Oklahoma under Bud Wilkinson. In the formation, the quarterback lines up with a fullback and two tailbacks behind him, and on any play may keep the ball, hand off to the fullback, or pitch to a tailback. From the time Bryant arrived at Alabama through the 1970 season, the Crimson Tide ran a pro-style offense. By 1969, Bryant began to recruit larger linemen and tailbacks, and after a pair of six win seasons in 1969 and 1970, Bryant saw the success of the wishbone for the Longhorns and decided to implement the offense for the 1971 season. In spring 1971, Alabama assistants Mal Moore and Jimmy Sharpe traveled to Austin where they saw first hand how the wishbone operated during Texas' final week of spring practice.
Link Information: was an American football player and coach. He served as the head coach at Mississippi State University (19541955), Answer: 12
Output:
How long had Darrell Royal been working as a head coach the year he learned about the wishbone offense?