Assume that number of ticket of denomination $20 sold= n.

Since 8000 tickets were sold in all, the number of tickets of denomination $30 sold = 8000-n.

Total Revenue generated is 20n +30(8000-n) = 209000 $

Solve the equation as 20n-30n= 209000-240000

-10n =-31000

Hence n= 3100.

Thus 20$ Tickets sold are 3100 and 30$ Tickets sold are 4900.

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