Given:
There are 8,000 seats at this venue.
There is a lawn that is rectangular 100 ft by 400 ft.
One person takes up 2.5 square ft.
To find number of tickets to be sold:
Area of the rectangular lawn is,
Number of persons those who occupies the rectangular lawn is,
Hence, the total number of tickets to be sold is,
8000+16000=24000 tickets.
Hence, the answer is, 24000 tickets.