Question: The City of Onkaparinga has a council that has area offices situated in the suburb approximately how far from the city center?

Context paragraphs:
City of Onkaparinga: The City of Onkaparinga is a local government area (LGA) located on the southern fringe of Adelaide, South Australia.  It is named after the Onkaparinga River, whose name comes from "Ngangkiparinga", a Kaurna word meaning women's river.  It is the largest LGA in South Australia, with an estimated population of 164,800 people in both urban and rural communities and is also geographically expansive, encompassing an area of 518.3 km².  The council is headquartered in the Noarlunga Centre with area offices situated in Aberfoyle Park, Woodcroft and Willunga.

Waterloo Corner, South Australia: Waterloo Corner is a rural/urban suburb approximately 22 kilometres north of Adelaide, the capital city of South Australia.  Most of the land is used for agricultural purposes, including wheat, olives, grapes and tomatoes.  Port Wakefield Road, and thus a lot of heavy freight, traverses the suburb.

First National Bank of Mason City: The First National Bank of Mason City, also known as Norwest Bank Building and City Center of Mason City, is a historic building located in Mason City, Iowa, United States.  It was designed by the Des Moines architectural firm of Liebbe, Nourse & Rasmussen, and it was the only Mason City commission for this firm.  Completed in 1911, it was constructed by C.E. Atkinson of Webster City, Iowa who had built several other H.F. Liebbe designs.  The 6½-story building follows the Early Commercial style.  It features modestly decorated main floor and attic level with five floors of rather plain brick construction in between.  The bank occupied most of the first floor and some of the office space above, while the other office space was taken up by professional offices.  By the 1960s the bank occupied the whole building.  John Dillinger, Baby Face Nelson, John Hamilton and Tommy Carroll robbed the bank on March 13,1934 and stole about $50,000.  Dillinger was wounded in an exchange of gunfire during the heist.  The building to the north of the bank was torn down in 1982 and a two-story annex to the bank replaced it.  The bank building was individually listed on the National Register of Historic Places in 1997, and as a contributing property in the Mason City Downtown Historic District in 2005.  City Center of Mason City Inc. bought the building in 1995, and remodeled it into apartments and offices.

Onkaparinga Hills, South Australia: Onkaparinga Hills is a southern suburb of Adelaide, in the City of Onkaparinga.  It covers an area of approximately 22 km2 .  It has a population of 2534 people (2011 Census).  It is a leafy suburb that includes parts of the Onkaparinga River National Park.

Bagsværd: Bagsværd (] ) is a lower middleclass suburb approximately 12 km northwest of Copenhagen, in the Gladsaxe Municipality.  Its center is dominated by the Bagsværd Towers, two high-rise apartment blocks.  The suburb is connected by S-Train and has three stations: Skovbrynet, Bagsværd, and Stengården.

Redbank Plains, Queensland: Redbank Plains is a suburb approximately 30 km from the Brisbane CBD.  Located on the outskirts of the Brisbane Statistical Division, its Local Government Area is the City of Ipswich.  At the 2016 Census the suburb recorded a population of 19,299.  Redbank Plains is not to be confused with the neighbouring suburb Redbank.

Aberfoyle Park, South Australia: Aberfoyle Park is a suburb in the City of Onkaparinga in the state of South Australia.  It is located in the southern suburbs of Adelaide, approximately 20 km from the city centre.  Aberfoyle Park has a shopping mall called "The Hub", several primary schools and a public high school, one of the biggest in the state.

Saunders Beach, Queensland: Saunders Beach is a residential suburb approximately 25 km north of the Townsville, Queensland, Australia.  The Saunders Beach community is situated just south-east of the mouth of Althaus Creek, the beach itself stretching approximately 6 km further south-east to the mouth of Black River.

Hvissinge: Hvissinge (or Hvessinge on some maps, though not in local signage) is a suburb approximately 13 km west of central Copenhagen.  Originally a small village, but in the 1970s the town grew quickly along with Glostrup.  It is part of Glostrup Municipality and situated 2 km north east of the city centre.

St. John the Baptist Byzantine Catholic Cemetery: St. John the Baptist Byzantine Catholic Cemetery is an Eastern Catholic cemetery in Bethel Park, Pennsylvania, United States, a suburb approximately 5 mi south of downtown Pittsburgh.  It is situated on a hillside in the southwest corner of the intersection of Connor Road and Pennsylvania State Route 88.

Supporting paragraphs: City of Onkaparinga Aberfoyle Park, South Australia
Answer: 20 km