Question: The sixth single off of 2Pac's fourth studio album features what contemporary soul singer?
Context: 2Pacalypse Now is the debut studio album by American rapper 2Pac.  It was released on November 12, 1991, by Interscope Records and EastWest Records America.  Less polished than it later proceed with his studio album, "2Pacalypse Now", which is 2Pac's commentary on contemporary social issues facing American society such as: racism, police brutality, poverty, black on black crime, and teenage pregnancy, some issues giving a lyrical glimpse into the world of a young black man on the urban streets of the United States.  It featured three singles; "Brenda's Got a Baby", "Trapped", and "If My Homie Calls".  "2Pacalypse Now" was certified Gold by the Recording Industry Association of America (RIAA). My Homies is the fifth studio album by American rapper Scarface.  The album was released March 3, 1998, by Rap-A-Lot Records.  The album features production by Mike Dean, Mr. Lee, N.O. Joe, Scarface and Tone Capone.  It peaked at number 1 on the "Billboard" Top R&B/Hip-Hop Albums and at number 4 on the "Billboard" 200 and was certified Platinum by the RIAA on April 6, 1998.  The album features guest performances by 2Pac, Master P, Ice Cube, Devin the Dude, B-Legit, UGK, Too Short, Do or Die and Willie D.  Scarface appears solo on two of thirty songs, performs with others on twenty-three and does not contribute vocals on five.  A sequel to the album, "My Homies Part 2", was released on March 7, 2006. "Playa Cardz Right" is a song by American R&B recording artist Keyshia Cole.  The song features late rapper 2Pac and was originally included on his sixth posthumously released album "Pac's Life" (2006), with most of his vocals initially recorded for his fifth studio album "All Eyez on Me" (1996).  Cole's reworked version, produced by Ron Fair and Carvin & Ivan for Karma Productions, was released as the lead single from her third album "A Different Me" (2008). Danny Boy Steward (born October 31, 1977) is a Chicago native known by his stage name Danny Boy or DB.  He is a contemporary African-American soul singer originally signed for a five-year run with Death Row Records by Suge Knight.  He made his debut on 1994's Murder Was the Case soundtrack with the R&B charter Come When I Call (Produced by DJ Quik).  In 1995, he released his first single entitled Slip N Slide (Produced by Reggie Moore and co-produced by DeVante Swing) with then unknown artist Ginuwine singing the chorus.  The video was shot in Cabo, and also features scenes with 2Pac, Snoop Dogg, Nate Dogg and Tha Dogg Pound.  Danny is best known for singing the choruses of the 2Pac songs "I Ain't Mad at Cha", "What'z Ya Phone #", "Picture Me Rollin'" and "Heaven Ain't Hard 2 Find" on All Eyez on Me, as well as "Toss It Up" on .  He had recorded several albums' worth of music while on Death Row Records, but none were released during his time there. Restless is the third studio album by rapper Trae.  It was released on June 27, 2006.  This is Trae's first album to be released on Rap-A-Lot Records.  The track entitled "The Truth" features 2Pac's verse from the song "Dumpin".  It is taken from 2Pac's posthumously released album "Pac's Life".  About.com named Restless one of the Top 100 Rap Albums of the 2000s. Tupac: Resurrection was released by Amaru Entertainment as the soundtrack for the 2003 documentary, Academy Award nominated "".  It includes several previously released 2Pac recordings, including "Death Around the Corner" from "Me Against the World", "Secretz of War" from "Still I Rise", Holler If Ya Hear Me from "Strictly 4 My N.I.G.G.A.Z." and "Rebel of the Underground" from "2Pacalypse Now"; and unreleased 2Pac verses re-constructed into new tracks such as "Ghost", "One Day at a Time", and "Runnin (Dying to Live)".  Eminem produced major parts of this album.  The song "Runnin (Dying to Live)" won the Top Soundtrack Song of the Year award at the 2005 ASCAP Rhythm & Soul Music Awards.  The Album Features The Notorious B.I.G., Eminem, 50 Cent, Outlawz, & Digital Underground.  "Intro", "Ghost", "Death Around The Corner", "Bury Me A G" and "Str8 Ballin'" do not actually feature in the movie, but appear on the album. "Are U Still Down" is a song co-written and performed by American contemporary R&B singer Jon B, issued as a promotional single from his second studio album "Cool Relax".  It was commissioned as a double single with "They Don't Know" in some markets.  The song features a rap by American hip hop musician 2Pac; and it was the final rap verse that 2Pac recorded before his death for a collaboration. Tha Hall of Game is the third studio album by American rapper E-40, released October 29, 1996, on Jive and Sick Wid It Records.  The album features production by Ant Banks, Mike Mosley, Rick Rock, Studio Ton and Tone Capone.  It peaked at number 2 on the "Billboard" Top R&B/Hip-Hop Albums and at number 4 on the "Billboard" 200.  One single, "Things'll Never Change"/"Rapper's Ball", peaked at number 19 on the "Billboard" Hot R&B/Hip-Hop Songs.  and performed well on several other charts as well.The album was certified gold in 1997 by the RIAA.  The album features guest performances by fellow members of The Click: B-Legit, D-Shot and Suga-T, as well as 2Pac, Luniz, Cold 187um, Kokane, Keak da Sneak and Levitti. "I Ain't Mad at Cha" is a song by rapper 2Pac released shortly after his death as the sixth single from his album "All Eyez on Me".  It was also his last single using the stage name 2Pac.  The song features contemporary soul singer Danny Boy who provided the vocals for the song's hook.  The song did well in the United Kingdom, reaching the number 13 on the UK Singles Chart and on the UK R&B Charts peaking at number 3. All Eyez on Me is the fourth studio album by American rapper 2Pac and the last one to be released during his lifetime.  It was released on February 13, 1996, by Death Row Records and Interscope Records.  The album featured the "Billboard" Hot 100 #1 singles "How Do U Want It" and "California Love".  It featured five singles in all, the most of any of Shakur's albums.  Moreover, "All Eyez on Me" (which was the only Death Row Records release to be distributed through PolyGram by way of Island Records) made history as the first double-full-length hip-hop solo studio album released for mass consumption.  It was issued on two compact discs and four LPs.
Answer: Danny Boy