The 2016 Stockton ATP Challenger was a professional tennis tournament played on hard courts.
 It was the first edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Stockton, United States between 1 October and 9 October 2016.
Happy Valley is a metropolitan suburb of Adelaide, South Australia.
 It is located 20 km south of the Central Business District of Adelaide.
The 2016 Poprad-Tatry ATP Challenger Tour was a professional tennis tournament played on clay courts.
 It was the second edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Poprad, Slovakia between 13 and 18 June 2016.
The 2016 Santaizi ATP Challenger was a professional tennis tournament played on indoor carpet courts.
 It was the third edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Taipei, Taiwan between 25 April and 1 May.
The 2016 Gemdale ATP Challenger was a professional tennis tournament played on hard courts.
 It was the third edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Shenzhen, China between 21 and 27 March 2016.
The 2016 ATP Challenger Torino was a professional tennis tournament played on clay courts.
 It was the second edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Turin, Italy between 18 and 24 April.
The 2016 City of Onkaparinga ATP Challenger was a professional tennis tournament played on hard courts.
 It was the second edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Happy Valley, Australia between 2–10 January 2016.
The 2016 Latrobe City Traralgon ATP Challenger is a professional tennis tournament played on outdoor hard court.
 It is the fifth edition of the tournament which was part of the 2016 ATP Challenger Tour.
 It took place in Traralgon, Australia between 24–30 October 2016.
The 2015 City of Onkaparinga ATP Challenger was a professional tennis tournament played on hard courts.
 It was the first edition of the tournament which was part of the 2015 ATP Challenger Tour.
 It took place in Happy Valley, Australia between 3–11 January 2015.
The 2017 City of Onkaparinga ATP Challenger was a professional tennis tournament played on hard courts.
 It was the third edition of the tournament and part of the 2017 ATP Challenger Tour.
 It took place in Happy Valley, Australia from 2 to 8 January 2017.

Question: The 2016 City of Onkaparinga ATP Challenger took place in a metropolitan suburb how far south of the Central Business District of Adelaide?
Answer: 20 km