Background: James Paul McCartney was born on 18 June 1942 in Walton Hospital, Liverpool, England, where his mother, Mary Patricia (nee Mohin), had qualified to practise as a nurse. His father, James ("Jim") McCartney, was absent from his son's birth due to his work as a volunteer firefighter during World War II. McCartney has one younger brother named Michael.
Context: McCartney was inducted into the Rock and Roll Hall of Fame in 1988 as a member of the Beatles and again as a solo artist in 1999. In 1979, the Guinness Book of World Records recognised McCartney as the "most honored composer and performer in music", with 60 gold discs (43 with the Beatles, 17 with Wings) and, as a member of the Beatles, sales of over 100 million singles and 100 million albums, and as the "most successful song writer", he wrote jointly or solo 43 songs which sold one million or more records between 1962 and 1978. In 2009, Guinness World Records again recognised McCartney as the "most successful songwriter" having written or co-written 188 charted records in the United Kingdom, of which 91 reached the top 10 and 33 made it to number one.  McCartney has written, or co-written 32 number-one singles on the Billboard Hot 100: twenty with the Beatles; seven solo or with Wings; one as a co-writer of "A World Without Love", a number-one single for Peter and Gordon; one as a co-writer on Elton John's cover of "Lucy in the Sky with Diamonds"; one as a co-writer on Stars on 45's "Medley"; one as a co-writer with Michael Jackson on "Say Say Say"; and one as writer on "Ebony and Ivory" performed with Stevie Wonder. As of 2009, he has 15.5 million RIAA certified units in the United States as a solo artist plus another 10 million with Wings.  Credited with more number ones in the UK than any other artist, McCartney has participated in twenty-four chart topping singles: seventeen with the Beatles, one solo, and one each with Wings, Stevie Wonder, Ferry Aid, Band Aid, Band Aid 20 and "The Christians et al." He is the only artist to reach the UK number one as a soloist ("Pipes of Peace"), duo ("Ebony and Ivory" with Wonder), trio ("Mull of Kintyre", Wings), quartet ("She Loves You", the Beatles), quintet ("Get Back", the Beatles with Billy Preston) and as part of a musical ensemble for charity (Ferry Aid).  "Yesterday" is one of the most covered songs in history with more than 2,200 recorded versions, and according to the BBC, "the track is the only one by a UK writer to have been aired more than seven million times on American TV and radio and is third in the all-time list ... [and] is the most played song by a British writer [last] century in the US". His 1968 Beatles composition "Hey Jude" achieved the highest sales in the UK that year and topped the US charts for nine weeks, which is longer than any other Beatles single. It was also the longest single released by the band and, at seven minutes eleven seconds, was at that time the longest number one. "Hey Jude" is the best-selling Beatles single, achieving sales of over five million copies soon after its release.  In July 2005, McCartney's performance of "Sgt. Pepper's Lonely Hearts Club Band" with U2 at Live 8 became the fastest-released single in history. Available within forty-five minutes of its recording, hours later it had achieved number one on the UK Official Download Chart.
Question: what was one of his best selling singles?. Whats the answer?
duo ("Ebony and Ivory" with Wonder),