Question: How many number-one hit singles in the US did the producer of the album Harbor produce?

John Clifford Farrar ( ; born 8 November 1945) is an Australian-born music producer, songwriter, arranger, singer and guitarist.  As a musician, Farrar is a former member of several rock and roll groups including The Mustangs (1963–64), The Strangers (1964–70), Marvin, Welch & Farrar (1970–73), and The Shadows (1973–76); in 1980 he released a solo eponymous album.  As a songwriter and producer he worked with Olivia Newton-John from 1971 to 1989.  He wrote her number-one hit singles: "Have You Never Been Mellow" (1975), "You're the One That I Want" (1978 duet with John Travolta), "Hopelessly Devoted to You" (1978), and "Magic" (1980).  He also produced the majority of her recorded material during that time including her number-one albums, "If You Love Me, Let Me Know" (1974), "Have You Never Been Mellow" (1975) and "Olivia's Greatest Hits Vol.  2" (1982); and he was a co-producer of "" (1978) – the soundtrack for the film of the same name.  Farrar also produced Newton-John's first United States number-one hit single, "I Honestly Love You", which was awarded the Grammy Award for Record of the Year in 1975.  In 1969 Farrar married fellow Australian singer, Pat Carroll – formerly Newton-John's singing partner.  In July 1970 Farrar and Carroll relocated to the United Kingdom and from late 1975 they have resided in the US.  They are the parents of Sam Farrar (Phantom Planet bassist and Maroon 5 touring member) and Max Farrar (Golden Ghost guitarist and keyboardist). <SEP>  He was referred to as the "Fifth Beatle", including by Paul McCartney, in reference to his extensive involvement on each of the Beatles' original albums. Sir George Henry Martin {'1': ", '2': ", '3': ", '4': "} (3 January 19268 March 2016) was an English record producer, arranger, composer, conductor, audio engineer, and musician.  Martin produced 30 number-one hit singles in the United Kingdom and 23 number-one hits in the United States. <SEP> Harbor is the seventh original studio album by American folk rock trio America, released by Warner Bros.  Records in February 1977.  It was the last to feature Dan Peek, who embarked on a solo Christian career shortly after the album's release.  The album was produced by George Martin. <SEP> James Nelson Williams (born January 21, 1962), known by the stage name D Train, is an American singer, songwriter, instrumentalist, producer and actor.  He rose to fame in the early 1980s with the release of his first album “You're the One for Me” (working with songwriter/producer Hubert Eaves III initially as a duo), which spawned his first US "Billboard" Dance chart number-one hit, "You're the One for Me".  His debut album (under the Prelude Records label) would also chart with the hits "Keep On" and the much covered Burt Bacharach hit "Walk on By".  He would go on to work with Eaves producing hits on the follow-up albums "Music" and "Something's On Your Mind" before being signed to Columbia Records, producing more hit singles on the albums "Miracles of the Heart" and "In Your Eyes".  The two parted ways in 1988 and D Train went on to perform on his own label, releasing albums such as "701 Franklin Ave.".