Because the cost of a concert is almost fixed, the change in total cost per additional spectator is almost 0. That is, the marginal cost is 0. Economically, when MR is greater than MC, an increase in production and sales here as (spectators) results in an increase in total profit, so each additional spectator increases total profit. But the limit of increase in audience is the number of seats in the arena, so. The number of seats in the arena is the ideal number of spectators for the performance company to bring in the maximum profit.