Question: How many properties are maintained by the amusement park corporation that first screened the film The Sensorium in 1984?

Context paragraphs:
Shishu Park: Shishu Park (Bengali: ঢাকা শিশু পার্ক ) is the only public sector children's amusement park in Shahbag, Dhaka, Bangladesh.  Established in 1979 on 15 acre of land, it is the first children's amusement park in Bangladesh.  Established as a profit making venture by Bangladesh Parjatan Corporation, the government-owned tourism promotion agency in Bangladesh, it is maintained by Dhaka City Corporation as its only entertainment park since 1983.  The 12 rides of the park include including a wheel train, a merry-go-round and a number of wheel-based rides.  Bangladesh Air Force donated a fighter jet in 1992.  The cheapest of all entertainment parks in Dhaka, charging BDT 8.00 for entry and 6.00 for each ride, it draws about 6,000 visitors a day.  During the Eid-ul-Fitr holidays the number of visitors reach up to 350 thousands.  The City Corporation earns about BDT 200 million annually from the park.  The park is open Monday through Thursday and Saturday from 2:00 pm to 7:00 pm.  On Fridays, it is open from 2:30 pm to 7:30 pm.

Wonderland City: Wonderland City was an amusement park located at Tamarama, on Wonderland Avenue near the point at which it joins Fletcher Street, in Sydney, Australia.  It opened on Saturday, 1 December 1906 and closed in 1911.  At the time it was the largest open air amusement park in the southern hemisphere.  The 20 acre amusement park was operated by theatrical entrepreneur William Anderson.  During its operation the colossal playground had a balloon could go up to about 3,800 feet (1158.24 meters) high.  An enormous switchback railway and around the clifftop, a steam-driven miniature railway operated over about two miles (3.218688 km) of track.  A large wooden bridge build over an artificial lake, the Alpine Slide would take you to "Rivers of the World", Seal Pond.  An open air Roller Skating Ring, American Shooting Gallery.  It was operated by electric light powered by its own steam plant, and the whole area was covered with thousands of gaily coloured lamps and described as a Fairy City.  The first Surf "Gymkhana" Carnivals was held at Wonderland City (Tamarama Beach) organised by Bondi SBLSC on Saturday 11 February 1908.  was dogged by controversy for its attempts using high barbed-wire fence blocked access completely to local swimmers from Tamarama Beach.  Before being occupied by the amusement park, Tamarama Park was the site of The Royal Aquarium and Pleasure Grounds, commonly called the Bondi Aquarium.

Family entertainment center: A family entertainment center (or centre), often abbreviated FEC in the entertainment industry, (also known as indoor amusement park or indoor theme park) is a small amusement park marketed towards families with small children to teenagers, and often entirely indoors or associated with a larger operation such as a theme park.  They usually cater to "sub-regional markets of larger metropolitan areas."  FECs are generally small compared to full-scale amusement parks, with fewer attractions, a lower per-person per-hour cost to consumers than a traditional amusement park, and not usually major tourist attractions, but sustained by an area customer base.  Many are locally owned and operated, although there are a number of chains and franchises in the field.  FECs are sometimes called family amusement centers, play zones, family fun centers, or simply fun centers.  Some non-traditional FECs, called urban entertainment centers (UECs), with more customized and branded attractions and retail outlets, are associated with major entertainment companies and may be tourist destinations.  Others, sometimes operated by Non-Profit organizations as Children's Museums or Science Centers, tend to be geared toward edutainment experiences rather than simply amusement.  FECs may also be adjuncts to full-scale amusement parks.

Wild Waves Theme Park: Wild Waves Theme & Water Park is an amusement park and water park in Federal Way, Washington.  Opened in 1977 as The Enchanted Village, the park is a popular summer destination in the Pacific Northwest and it is Washington's only water and amusement park.  The park's name was reverted to Wild Waves Water Park and Enchanted Village Amusement Park in April 2016, and once again changed to Wild Waves Theme and Water Park in November 2016, as a result of the park's acquisition by EPR Properties.

LeSourdsville Lake Amusement Park: LeSourdsville Lake Amusement Park was an amusement park located in Middletown, Ohio.  Opening in 1922 as a family picnic and campground, LeSourdsville Lake transformed in the 1940s to an amusement park with rides, attractions, and an arcade.  In 1977, the name was changed to Americana Amusement Park.  Following an electrical fire in 1990 that caused over $5 million in damages, the park fell into decline and was eventually closed in 1999.  Under new ownership, the park briefly opened again in 2002 returning to the name "LeSourdsville Lake Amusement Park", but after failed attempts to turn a profit and the operating company going bankrupt, it closed permanently near the end of the 2002 season.  The park's remaining rides and attractions were either demolished or sold, or still sit today.

Six Flags: Six Flags, officially Six Flags Entertainment Corporation, is an amusement park corporation based in the United States, with properties in the US, Canada, and Mexico.  It is the largest amusement park company in the world, based on the number of properties owned, and is ranked sixth in terms of attendance.  The company maintains twenty properties throughout North America including theme parks, thrill parks, water parks, and family entertainment centers.  In 2016, Six Flags properties hosted over 30.1 million guests.

White City (Indianapolis): White City (also known as White City Amusement Park) was an amusement park in Indianapolis, Indiana's Broad Ripple Park that was in operation from May 26, 1906 until June 26, 1908.  The trolley park was constructed and owned by the Broad Ripple Transit Company.  Similar to nearby rivals Riverside Amusement Park and Wonderland, White City was inspired by an exhibit in the 1893 World's Columbian Exposition in Chicago.  Although the park's grand opening was immensely successful, White City's existence was the briefest of the three, having been open for two and one-half seasons before burning to the ground.  Throughout the park's existence, advertisements touted White City as "the amusement park that satisfied."

Parque de Diversiones: The Parque Diversiones Dr. Roberto Ortiz Brenes (English: National Amusement Park Dr. Roberto Ortiz Brenes ; also known as Parque Diversiones) is an amusement park located in San José, Costa Rica.  The park's motto is "healthy children helping healing children".  The park was named for Dr. Brenes because it was his proposal which resulted in it being established.  His idea was that the profits from the amusement park would assist to support the National Children's Hospital "Dr. Carlos Saénz Herrera", which was established in 1964.  The National Amusement Park began operating at the end of 1981.

Wonderla: Wonderla Holidays Limited is a leading amusement park designing and operating company in India headquartered near Bidadi, 28 km from Bengaluru.  It is promoted by Kochouseph Chittilappilly and his son Arun Chittilappilly.  Wonderla's flagship amusement park located at the same address is the second theme park project from the company and has been operational since October 2005.  It is spread over an area of 82 acre .  The first amusement park, Wonderla Kochi, was set up in 2000.  The third amusement park project Wonderla Hyderabad was commissioned in April 2016.  The parks have been set up with a total investment of over .

The Sensorium: The Sensorium is regarded the world's first commercial 4D film and was first screened in a Six Flags theme park in Baltimore in 1984.  It was produced in partnership with Landmark Entertainment.

Supporting paragraphs: The Sensorium Six Flags
Answer: twenty