The correct level of output for a profit-maximizing, monopolistically competitive firm always matches the point where

total revenue equals total cost.
marginal revenue equals marginal cost.
price equals average total cost.
price equals marginal cost.
average revenue equals marginal revenue.

Marginal revenue equals marginal cost

Explanation:

The profit maximizing level of output is when the revenue generated by producing an additional unit equals the cost of producing this additional unit. That is when,

Marginal revenue = Marginal cost.

At this point if a firm produces any more there is an added cost of producing the additional unit and total profits for the firms decrease and if they produce any less than this, the firm is forgoing profits that it could earn.

Of course, monopolistically competitive firms can still in someway influence their prices, but the always chose to produce at the profit maximizing level of output.

This is also called the optimum efficient level of production.

Hope that helps.

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