Question: Edward Jackson was the head coach for Howard University and two other schools for how long

Context paragraphs:
Edward Jackson (American football): Edward L. Jackson was an American football head coach for several historically black colleges and universities in the Eastern United States.  He was the head coach at Delaware State University, Johnson C. Smith University and Howard University, altering his tenures among the three schools over the course of 23 years.  Jackson compiled an overall record of 141–62–12, including two conference championships at Delaware State in 1934 and 1956.  Only once during his coaching career did a team of his finish with a sub-.500 record, when Delaware State finished 1–3–1 in 1936.

2013 Howard Bison football team: The 2013 Howard Bison football team represented Howard University in the 2013 NCAA Division I FCS football season.  They were led by interim head coach Rayford Petty, who was conducting the season after Gary Harrell took a leave of absence for the 2013 season.  Petty was previously head coach at Howard from 2002–2006, compiling a 25–30 record in those 5 seasons.  Harrell plans to return for the 2014 season.  The Bison played their home games at William H. Greene Stadium.  They were a member of the Mid-Eastern Athletic Conference.

Howard University: Howard University (HU or simply Howard) is a federally chartered, private, coeducational, nonsectarian, historically black university (HBCU) in Washington, D.C. It is recognized by the Carnegie Foundation as a research university with high research activity and is accredited by the Middle States Commission on Higher Education.

Cathy Parson: Catherine "Cathy" Parson (born May 4, 1961) is a women's basketball coach.  In 2013, Parson was selected as head coach of Frostburg State University's women's basketball team.  Before landing at Frostburg State, Parson spent eight seasons as the head coach at Howard University, where she compiled a 99-100 record in her first seven seasons.  She led the Lady Bison to two regular season MEAC titles.  The 2001 team won the MEAC tournament title.  In both 2000 and 2001, she was named the MEAC coach of the year.

Mike London: Michael Wilson "Mike" London, Sr. (born October 9, 1960) is the current head football coach for the Howard Bison football program at Howard University in Washington, D.C. He is a former defensive back and associate head coach and defensive line coach for the University of Maryland, College Park.  Prior to Maryland, London was the head coach of the Virginia Cavaliers football program of the University of Virginia.  A native of the Hampton Roads area of Virginia, London played college and pro football as a defensive back for the Richmond Spiders and Dallas Cowboys.  He was a police officer and detective in Richmond, Virginia with the city's street crimes unit before pursuing a coaching career.

Willie Jeffries: Willie E. Jeffries, (born January 4, 1937) is a former American football player and coach.  He served as the head football coach at South Carolina State University for 19 seasons in two stints (1973–1978, 1989–2001), five seasons at Wichita State University (1979–1983), and five seasons at Howard University (1984–1988).  Jeffries was the first African American head coach of a NCAA Division I-A football program at a predominantly white college when he coached Wichita State.  He was elected to the College Football Hall of Fame in 2010.

Rayford Petty: Rayford Tilman Petty is an American college football coach and former player.  He is currently the defensive coordinator at Howard University, a position he has held since the 2011 season.  Petty served as head coach at Howard from 2002 to 2006, and again in an interim capacity in 2013, compiling an overall record of 31 wins and 36 losses.  His career also includes positions as an assistant coach at North Carolina A&T University, Southern University, Norfolk State University and Delaware State University.  A graduate of Elon University, Petty played as a linebacker for the Phoenix during the late 1970s.

Steve Wilson (defensive back): Steven Anthony Wilson (born August 24, 1957) is a former American football defensive back in the National Football League for the Dallas Cowboys and Denver Broncos.  He played college football at Howard University.  He was the former head football coach at his alma mater Howard University, from 1989 to 2001, and Texas Southern University, from 2004 to 2007.

Phillip Gyau: Phillinoisip "Phillip" Gyau (born February 7, 1966) is a former U.S. soccer forward who is the current head coach of the Howard Bison men's soccer program.  He spent his outdoor career in the American Soccer League and the American Professional Soccer League, his indoor career with the Washington Warthogs and Baltimore Blast, and spent nine years with the U.S. National Beach Soccer team.  He earned six caps with the U.S. national team.  In 2014, he became the head coach for Howard University's soccer team.  Gyau is also the father of U.S. international Joe Gyau.

Kevin Nickelberry: Kevin Nickelberry (born (1964--) 15, 1964 ) is an American college basketball coach and current head men's basketball coach at Howard University, named to the position on April 25, 2010.  He had previously been head coach at Hampton University.

Supporting paragraphs: Edward Jackson (American football) Howard University
Answer: 23 years