Number of Machines in use
 Number of bets placed on a machine per hour
 hours each machine is in operation and being bet at the average bet rate and average bet listed above
 8.7 Million People over 18 in Illinois
 Calculated by the average bet and average bets per hour
 In hours
I have done a google spreadsheet here.
Assuming the tax rate is 30% on the net (earnings after payouts). To get to 236 Million a year of revenue there would have to be 100,000 machines (one for every 87 people over 18) being played with an average bet of $0.75 30 times an hour for 12 hours.
Or another way to think of it.
Every person over 18 would have to bet about $1,100 a year. At the average rate of betting listed above each person over 18 would have to spend 50 hours a year playing video poker.
Follow the link to see the sheet, if you want to edit it, let me know.