Answer: A monopolistic company will produce to the point where the marginal cost is equal to marginal income, which is the production point called optimal.
Marginal Income = Marginal Cost
In other words, from that point the company is not able to obtain more profit if it increases its production. Because it happens that the cost of producing one more unit is greater than the marginal income for that unit, it would be necessary to reduce the level of production because it is excessive.
As in a situation of perfect competition the company is accepting price, then it sells its product at the price given by the market, so its optimal point will be: Marginal Cost = Marginal Income = Price