Tracy Ann Austin Holt (born December 12, 1962) is an American former World No. 1 retired professional tennis player.
 She won three Grand Slam titles, including the women's singles titles at the 1979 and 1981 US Opens, and the mixed doubles title at the Wimbledon Championships in 1980.
 Additionally, she won the WTA Tour Championships in 1980 and the year-ending Toyota Championships in 1981, both in singles.
 A series of injuries and a serious automobile accident cut short her career.
 Since 1979, she has been the youngest US Open female singles champion in history, and she is the youngest inductee of all time at the International Tennis Hall of Fame.
 Austin won singles titles on all playing surfaces: clay (both red clay and green clay), indoor carpet, grass, and hard courts.
The 1999 US Open – Women's Singles was the women's singles event of the hundred-and-ninth edition of the US Open, the fourth and last Grand Slam of the year, and the most prestigious tournament in the Americas.
 Lindsay Davenport was the defending champion, but she was defeated in the semifinals by Serena Williams.
 Williams then won in the final, defeating World No. 1 Martina Hingis.
 This was Williams' first Grand Slam title, and she became the first African American woman to win a Grand Slam in the Open Era.
 She won five more titles in 2002, 2008, 2012, 2013 and 2014.
Bruno Fraga Soares (] ; born February 27, 1982, in Belo Horizonte) is a professional tennis player from Brazil.
 His highest singles ranking on the ATP Tour is World No. 221, which he reached in March 2004.
 Primarily a doubles specialist, his career-high doubles ranking is World No. 2, which he achieved in October 2016.
 After a few efforts, including a final in the 2012 US Open and the semifinals of the 2008 and 2013 French Opens, Soares finally won his first Grand Slam title at the 2016 Australian Open, partnering Jamie Murray and then followed that up with a second men's doubles title at the 2016 US Open.
 He has also won three Grand Slam titles in Mixed Doubles, two at the US Open, in 2012 and 2014, and one at the Australian Open in 2016.
 He was the third Brazilian tennis player to achieve this, after Maria Bueno and Thomaz Koch.
Billie Jean King and Martina Navratilova were the defending champions but only Navratilova competed that year with Pam Shriver.
Lucie Šafářová (] ; born 4 February 1987) is a Czech professional tennis player from Brno.
 She is currently the WTA world No. 1 doubles player.
 Šafářová has won seven WTA tour singles titles, fifteen doubles titles and reached the quarterfinals of the 2007 Australian Open by upsetting defending champion Amélie Mauresmo in the fourth round.
 She reached her first Grand Slam semifinal at the 2014 Wimbledon Championships and her first Grand Slam final at the 2015 French Open.
 She also won the 2015 Australian Open, 2015 French Open, 2016 US Open, 2017 Australian Open and 2017 French Open women's doubles titles partnering with Bethanie Mattek-Sands.
Pam Teeguarden (born April 17, 1951) is a former American professional tennis player in the 1970s and 1980s, ranked in the top 20 from 1970–1975, according to "John Dolan's Women's Tennis Ultimate Guide", prior to computer rankings.
 She won two Grand Slam Doubles Titles and was a quarter finalist in singles at the U.S. Open and The French Open.
 Her father Jerry, a well known coach, helped Margaret Court win the coveted Grand Slam (all four Grand Slam titles in one year) in 1970 and Virginia Wade to her 1977 Wimbledon triumph.
 Teeguarden was voted the "Most Watchable Player" based on play and appearance by a group of Madison Avenue advertising executives or "Mad Men" while playing at the US Open.
 Teeguarden played in 19 consecutive US Opens, holding the record until Chris Evert played in 20.
 She wore the first all black outfit in the history of tennis in 1975 at The Bridgestone Doubles Championships in Tokyo, starting a trend that is still popular today.
 Teeguarden was the first woman tennis player signed by Nike.
 She played on the victorious Los Angeles Strings Team Tennis team in 1981 and won the Team Tennis Mixed Doubles Division with Tom Gullikson in 1977; they were also runners-up in the league that year.
The 2012 US Open Men's Singles final was the championship tennis match of the Men's Singles tournament at the 2012 US Open.
 In the final, Andy Murray defeated defending champion Novak Djokovic 7–6, 7–5, 2–6, 3–6, 6–2 to win the match.
 It was the equal-longest US Open men's final in history, lasting 4 hours and 54 minutes (equalling the 1988 US Open final played by Ivan Lendl and Mats Wilander), and the equal second-longest men's final in the Open era, only behind the 2012 Australian Open final.
 By winning the 2012 US Open, Murray became the first British man since Fred Perry in 1936 to win a Grand Slam singles title, and the first British man in the Open Era to do so.
 The match is a significant part of the rivalry between the two players.
 This match also marked a milestone for Murray, as it was his 100th match win at a grand slam tournament.
Kenneth Robert Rosewall {'1': ", '2': ", '3': 'AM, MBE', '4': "} (born 2 November 1934) is a former world top-ranking amateur and professional tennis player from Australia.
 He won a record 23 tennis Majors including 8 Grand Slam singles titles and before the Open Era a record 15 Pro Slam titles and a record 35 Major finals overall.
 He won the Pro Grand Slam in 1963.
 Rosewall won 9 slams in doubles with a career double grand slam.
 He is considered to be one of the greatest tennis players of all time.
 He had a renowned backhand and enjoyed a long career at the highest levels from the early 1950s to the early 1970s.
 Rosewall was one of the two best male players for about nine years and was the World No. 1 player for a number of years in the early 1960s.
 He was ranked among the top 20 players, amateur or professional, every year from 1952 through 1977.
 Rosewall is the only player to have simultaneously held Pro Grand Slam titles on three different surfaces (1962–1963).
 At the 1971 Australian Open he became the first male player during the open era to win a Grand Slam tournament without dropping a set.
The Williams sisters are two professional American tennis players: Venus Williams (b. 1980), a seven-time Grand Slam title winner (singles), and Serena Williams (b. 1981), twenty-three-time Grand Slam title winner (singles), both of whom were coached from an early age by their parents Richard Williams and Oracene Price.
 There is a noted professional rivalry between them – between the 2001 US Open and the 2017 Australian Open tournaments, they met in nine Grand Slam singles finals.
 They became the first two players, female or male, to play in 4 consecutive grand slam singles finals from the 2002 French Open to the 2003 Australian Open; Serena famously won all 4 to complete the first of two "Serena Slams".
 Between 2000 and 2016, a 17-year span, they collectively won 12 Wimbledon singles titles (Venus won 5 and Serena won 7).
 By winning the 2001 Australian Open women's doubles title, they became the 5th pair to complete the Career Doubles Grand Slam and the only pair to complete the Career Doubles Golden Slam.
 At the time, Venus and Serena were only 20 and 19 years old, respectively.
 Since then they have gone on to add another two Olympic gold medals in the 2008 Beijing Olympics and the 2012 London Olympics.
 Nearly a decade later, the duo would go on to win 4 consecutive grand slam doubles titles from 2009 Wimbledon through 2010 Roland Garros, which would catapult them to co-No.
 1 doubles players on 7 June 2010.
 Two weeks later, on 21 June 2010, Serena would hold the No. 1 singles ranking and Venus would be right behind her at No. 2 in singles.
 Their most recent grand slam doubles titles came at the 2012 Wimbledon & 2016 Wimbledon events.
 They remain very close, often watching each other's matches in support, even after one of them has been knocked out of a tournament.
Billie Jean King ("née" Moffitt; born November 22, 1943) is an American former World No. 1 professional tennis player.
 King won 39 Grand Slam titles: 12 in singles, 16 in women's doubles, and 11 in mixed doubles.
 King won the singles title at the inaugural WTA Tour Championships.
 King often represented the United States in the Federation Cup and the Wightman Cup.
 She was a member of the victorious United States team in seven Federation Cups and nine Wightman Cups.
 For three years, King was the United States' captain in the Federation Cup.

Question: How many Grand Slam titles were won by the defending champion of the 1981 US Open - Women's Doubles?  
Answer: 39