Question: Bottom Line is an album by British bluesman John Mayall, an English blues singer, guitarist, organist and songwriter, whose musical career spans over how many years?

Context paragraphs:
Wake Up Call (John Mayall album): Wake Up Call is an album by British bluesman John Mayall (also called as an John Mayall & the Bluesbreakers album) with various special guest appearances by Buddy Guy, Mick Taylor, Mavis Staples and a few other musicians, released on April 6, 1993.

Empty Rooms: Empty Rooms is a studio album by English blues musician John Mayall, released in late 1969 on Polydor.  It is a follow-up to the live album The Turning Point, released earlier in the year with the same musicians: Jon Mark on acoustic guitar, Johnny Almond on saxophones and flute, and Stephen Thompson on bass.  John Mayall sings, plays harmonica, guitars and keyboards (including a moog synthesizer).  Former Canned Heat bassist Larry Taylor guests as second bass player on one track, "To a Princess," improvising with Thompson on an unusual bass duet.  The absence of a drummer leaves the rhythm rather fluid and the resulting sound is unusual, even for a John Mayall album.  The songs, all written by Mayall, mostly addressed his romance with photographer Nancy Throckmorton, a theme he would pursue further on "USA Union".

John Mayall &amp; the Bluesbreakers: John Mayall & the Bluesbreakers was an English blues rock band, led by singer, songwriter, and multi-instrumentalist John Mayall, OBE.  While never producing a radio-friendly hit on their own, the Bluesbreakers greatest legacy is as an incubator for British rock and blues musicians.  Many of the best known bands to come out of Britain in the 1960s and 1970s had members that came through the Bluesbreakers at one time, forming the foundation of British blues music that still appears heavily in classic rock radio.  Among those with a tenure in the Bluesbreakers are Eric Clapton and Jack Bruce (later of Cream), Peter Green, Mick Fleetwood, and John McVie (who would form Fleetwood Mac), Mick Taylor (the Rolling Stones), Aynsley Dunbar (Frank Zappa and The Mothers of Invention), and numerous other musicians.

Road Dogs (John Mayall album): Road Dogs is a studio album by British Bluesman John Mayall with the Bluesbreakers.  Recorded between January 10, 2005 and February 10, 2005 in Calabasas, California.

Spinning Coin: Spinning Coin is a studio album by the British bluesman John Mayall, with various session musicians.

Fabio Treves: Fabio Treves (born 27 November 1949) is an Italian blues musician.  Treves's nickname is "il Puma di Lambrate" (Lambrate's Cougar), mimicking the British bluesman John Mayall, known as the "Manchester's Lion".  Lambrate is the quarter of Milan where Treves grew up.

The 1982 Reunion Concert: The 1982 Reunion Concert is a live album from a concert by British Bluesman John Mayall.  His sidemen are Mick Taylor on guitar, John McVie on bass and Colin Allen on drums.  The concert took place at the Wax Museum, Washington DC, on 17 June 1982.  It was released in 1994 by Repertoire Records as a CD credited to John Mayall and the Bluesbreakers.

Bottom Line (album): Bottom Line is an album by British bluesman John Mayall with various musicians.  Along with "No More Interviews" it is one of only two Mayall albums that has never been released on CD.

John Mayall: John Mayall, OBE (born 29 November 1933) is an English blues singer, guitarist, organist and songwriter, whose musical career spans over fifty years.  In the 1960s, he was the founder of John Mayall & the Bluesbreakers, a band which has counted among its members some of the most famous blues and blues rock musicians.  They include Eric Clapton, Peter Green, Jack Bruce, John McVie, Mick Fleetwood, Mick Taylor, Don "Sugarcane" Harris, Harvey Mandel, Larry Taylor, Aynsley Dunbar, Hughie Flint, Jon Hiseman, Dick Heckstall-Smith, Andy Fraser, Johnny Almond, Walter Trout, Coco Montoya and Buddy Whittington.

Blues Breakers with Eric Clapton: Blues Breakers with Eric Clapton ( The Beano Album) is a 1966 blues/blues rock album recorded by John Mayall & the Bluesbreakers with Eric Clapton as part of the band.  It is the second album credited to John Mayall after the live "John Mayall Plays John Mayall".  Clapton left to form Cream after this recording, though would team up again in 1971 for the double LP "Back to the Roots".

Supporting paragraphs: Bottom Line (album) John Mayall
Answer: fifty