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

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. <SEP> 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.  In 2016, Six Flags properties hosted over 30.1 million guests.  The company maintains twenty properties throughout North America including theme parks, thrill parks, water parks, and family entertainment centers. <SEP> 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. <SEP> 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.