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

<P0-S0> Harbor is the seventh original studio album by American folk rock trio America, released by Warner Bros. <P0-S1>  Records in February 1977. <P0-S2>  It was the last to feature Dan Peek, who embarked on a solo Christian career shortly after the album's release. <P0-S3>  The album was produced by George Martin. <SEP> <P1-S0> 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. <P1-S1>  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. <P1-S2>  Martin produced 30 number-one hit singles in the United Kingdom and 23 number-one hits in the United States. <SEP> <P2-S0> James Nelson Williams (born January 21, 1962), known by the stage name D Train, is an American singer, songwriter, instrumentalist, producer and actor. <P2-S1>  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". <P2-S2>  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". <P2-S3>  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". <P2-S4>  The two parted ways in 1988 and D Train went on to perform on his own label, releasing albums such as "701 Franklin Ave.". <SEP> <P3-S0> John Clifford Farrar ( ; born 8 November 1945) is an Australian-born music producer, songwriter, arranger, singer and guitarist. <P3-S1>  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. <P3-S2>  As a songwriter and producer he worked with Olivia Newton-John from 1971 to 1989. <P3-S3>  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). <P3-S4>  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. <P3-S5>  2" (1982); and he was a co-producer of "" (1978) – the soundtrack for the film of the same name. <P3-S6>  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. <P3-S7>  In 1969 Farrar married fellow Australian singer, Pat Carroll – formerly Newton-John's singing partner. <P3-S8>  In July 1970 Farrar and Carroll relocated to the United Kingdom and from late 1975 they have resided in the US. <P3-S9>  They are the parents of Sam Farrar (Phantom Planet bassist and Maroon 5 touring member) and Max Farrar (Golden Ghost guitarist and keyboardist).