Michael Antonucci, Inc., owns a movie theater that has a seating capacity of 400.

The price of one ticket is $3. The theater is open 52 weeks a year, and attendance averages 4,200 a week.

Variable costs are $0.75 per person, and fixed annual costs are $131,040. Because consumer demand is far more than 400 seats for some movies, Antonucci is considering expanding the seating capacity to 600 for an additional annual fixed cost of $29,160. Variable costs per person will remain constant.

Required:

How much does average attendance have to increase to warrant the expansion if management wishes to maintain the same profit margin on sales? Show your calculations.