The Oklahoma City bombing was a domestic terrorist truck bombing on the Alfred P. Murrah Federal Building in downtown Oklahoma City, Oklahoma, United States on April 19, 1995.
 Perpetrated by Timothy McVeigh and Terry Nichols, the bombing killed 168 people, injured more than 680 others, and destroyed one-third of the building.
 The blast destroyed or damaged 324 other buildings within a 16-block radius, shattered glass in 258 nearby buildings, and destroyed or burned 86 cars, causing an estimated $652 million worth of damage.
 Extensive rescue efforts were undertaken by local, state, federal, and worldwide agencies in the wake of the bombing, and substantial donations were received from across the country.
 The Federal Emergency Management Agency (FEMA) activated eleven of its Urban Search and Rescue Task Forces, consisting of 665 rescue workers who assisted in rescue and recovery operations.
 The Oklahoma City bombing was the deadliest terrorist attack on American soil until the September 11 attacks six years later, and it still remains the deadliest incident of domestic terrorism in United States history.
The Oklahoma City Streetcar (OKC Streetcar), also known as the MAPS 3 streetcar, is a streetcar system currently under-construction in Oklahoma City, Oklahoma, United States.
 The 6.9 mi system will serve the greater downtown Oklahoma City area consisting of modern, low-floor streetcars.
 The initial system would see two lines that will connect Oklahoma City's Central Business District with the entertainment district, Bricktown, and the Midtown District.
 Expansion to other districts surrounding downtown as well as more routes in the CBD is already underway.
Downtown Oklahoma City is located at the geographic center of the Oklahoma City metropolitan area and contains the principal, central business district of the region.
 The CBD has over 51,000 workers and over 12000000 sqft of leasable office space to-date.
 Downtown Oklahoma City is the legal, financial, economic, nightlife, and entertainment center of the region.
The Oklahoma City Blazers were a professional ice hockey team based in Oklahoma City, Oklahoma, that played in the Central Hockey League.
 The Blazers played at the Ford Center, located in downtown Oklahoma City.
 On July 2, 2009, the Blazers ceased operations after failing to reach a lease agreement with the city.
Chesapeake Energy Arena, originally known as the Ford Center from 2002 to 2010 and Oklahoma City Arena until 2011, is an arena located in downtown Oklahoma City, Oklahoma, United States.
 It opened in 2002 and since 2008 has served as the home venue of the Oklahoma City Thunder of the National Basketball Association (NBA).
 Previously, Chesapeake Energy Arena was home to the Oklahoma City Blazers of the Central Hockey League (CHL) from 2002 until the team folded in July 2009, and the Oklahoma City Yard Dawgz of AF2 from 2004 to 2009 when the team moved to the Cox Convention Center.
 In addition to its use as a sports venue, Chesapeake Energy Arena hosts concerts, family and social events, conventions, ice shows, and civic events.
 The arena is owned by the city and operated by the SMG property management company and has 18,203 seats in the basketball configuration, 15,152 for hockey, and can seat up to 16,591 for concerts.
Eglin AFB Site C-6 is an Air Force Space Command radar station which houses the AN/FPS-85 phased array radar, associated computer processing system(s), and radar control equipment (e.g., MIT Radar Calibration System in 1996).
 Commencing operations in 1969, the AN/FPS-85 was the first large phased array radar.
 The entire radar/computer system is located at a receiver/transmitter building and is supported by the site's power plant, fire station, 2 water wells (for 128 people), and other infrastructure for the system.
 As part of the US Air Force's Space Surveillance Network its mission is to detect and track spacecraft and other manmade objects in Earth orbit for "the Joint Space Operations Center satellite catalogue".
 With a peak radiated power of 32 megawatts the Air Force claims it is the most powerful radar in the world, and can track a basketball-sized object up to 22,000 nautical miles from Earth.
Norman is a city in the U.S. state of Oklahoma 20 mi south of downtown Oklahoma City in its metropolitan area.
 The population was 110,925 at the 2010 census.
 Norman's estimated population of 120,284 in 2015 makes it the third-largest city in Oklahoma, and the city serves as the county seat of Cleveland County.
The Oklahoma City Crosstown Expressway, aka I-40 Crosstown, is a roughly 5 mi stretch of Interstate 40 (I-40) just south of Downtown Oklahoma City, running along the Oklahoma River between Agnew Avenue and the I-40/I-35/I-235 "Crossroads of America" junction.
 Prior to 2012, the I-40 Crosstown was an elevated stretch that bisected downtown.
 The Oklahoma City Crosstown is the defacto east–west artery through Oklahoma City, serving as an unofficial dividing line between north and south Oklahoma City (the official dividing line for address purposes is Sheridan Avenue).
 It is owned and maintained by the Oklahoma Department of Transportation (ODOT).
Oklahoma City University School of Law, also known as OCU Law, is one of the professional graduate schools of Oklahoma City University.
 OCU Law is located in Oklahoma City, Oklahoma and was founded in 1907.
 OCU Law was located in the Sarkeys Law Center on the southwest side of the Oklahoma City University campus until Spring 2015, when it moved to a new campus near downtown Oklahoma City.
The Radar Operations Center (ROC) is a National Weather Service (NWS) unit that coordinates the development, maintenance, and training for the NEXRAD weather radar network.
 It is located at the National Weather Center (NWC) in Norman, Oklahoma and run by the National Oceanic and Atmospheric Administration (NOAA) in the Department of Commerce with partners at the Department of Defense and the Department of Transportation.

Question: How far is the Radar Operations Center (ROC) from downtown Oklahoma City? 
Answer: 20 mi