Question: How long was mainstream career of the artist that toured along with the Baby Grandmothers?

Context paragraphs:
Gilgamesh Night: Gilgamesh Night (ギルガメッシュないと / ギルガメッシュ・ナイト ) was a softcore porn Japanese variety TV show broadcast from October 1991 to March 1998.  Airing Saturdays at 1:15 a.m. on TV Tokyo, the hour-long show helped launch the career of one of its late hosts, Ai Iijima, who afterwards moved into a more mainstream career.

Stevie Ray Vaughan: Stephen Ray Vaughan (October 3, 1954 – August 27, 1990) was an American musician, singer, songwriter, and record producer.  In spite of a short-lived mainstream career spanning seven years, he was one of the most influential guitarists in the revival of blues in the 1980s and one of the greatest guitarists of all time.  AllMusic describes him as "a rocking powerhouse of a guitarist who gave blues a burst of momentum in the '80s, with influence still felt long after his tragic death."

Ancient Heart: Ancient Heart is the debut studio album by Tanita Tikaram.  The record was initially released by Warner Music Group on 13 September 1988.  The album had huge success and was a hit globally, launching Tanita's mainstream career.  Guest musicians included Rod Argent, Mark Isham, Peter Van Hooke, Paul Brady, and Brendan Croker.  Argent and Van Hooke produced the album.  The record includes four singles.

Ernie Fields: Ernest Lawrence "Ernie" Fields (August 28, 1904 – May 11, 1997) was an African-American trombonist, pianist, arranger and bandleader.  He first became known for leading the Royal Entertainers, which were based in Tulsa, Oklahoma, and toured along a circuit stretching from Kansas City, Kansas, to Dallas, Texas.  In later years he led a band that recorded in Los Angeles.

Emergency fighter: An emergency fighter is an aircraft designed or adapted for use as a fighter during an emergency period in war.  While useful as a broad concept or definition, it is not easy to make the category of emergency fighter clear cut, as many aircraft designs are produced under pressure in wartime, and aircraft which were hastily adapted for use as fighters may then go on to have a mainstream career.

Baby Grandmothers: The Baby Grandmothers were a Swedish psychedelic rock band formed in Stockholm, Sweden, in 1967.  Established after the dissolution of the R&B band, the T-Boones, the group enjoyed a cult following as the house band at the popular psychedelic music club Filips.  Although the Baby Grandmothers rarely performed outside Sweden, the band did tour alongside Jimi Hendrix in 1968.  In the same year, the group recorded an album's worth of material, which appeared years later on their self-titled album.  The album is now considered an underground classic of experimental psychedelia.

Fisk Jubilee Singers: The Fisk Jubilee Singers are an African-American "a cappella" ensemble, consisting of students at Fisk University.  The first group was organized in 1871 to tour and raise funds for college.  Their early repertoire consisted mostly of traditional spirituals, but included some Stephen Foster songs.  The original group toured along the Underground Railroad path in the United States, as well as performing in England and Europe.  Later 19th-century groups also toured in Europe.

Bad Books: Bad Books is an American indie rock band formed in early 2010, and is composed of indie folk artist Kevin Devine and members of indie rock band Manchester Orchestra along with drummer Benjamin Homola.  The collaboration began when Kevin toured along with Manchester Orchestra in November–December 2008 in support of his EP "I Could Be with Anyone", and followed by the release of the split EP entitled "I Could Be the Only One" in January 2010.

Jimi Hendrix: James Marshall "Jimi" Hendrix (born Johnny Allen Hendrix; November 27, 1942 – September 18, 1970) was an American rock guitarist, singer, and songwriter.  Although his mainstream career spanned only four years, he is widely regarded as one of the most influential electric guitarists in the history of popular music, and one of the most celebrated musicians of the 20th century.  The Rock and Roll Hall of Fame describes him as "arguably the greatest instrumentalist in the history of rock music".

Dany Verissimo--Petit: Dany Verissimo-Petit (born June 27, 1982), is a French actress and model.  She briefly worked as a pornographic performer under the stage name Ally Mac Tyana, before starting a mainstream career, using first the name Dany Verissimo.

Supporting paragraphs: Baby Grandmothers Jimi Hendrix
Answer: four years