Suppose a tminus−shirt manufacturer currently sells 5,000 tminus−shirts per week and makes a profit of $10,000 per week. a manager at the plant observes, "although the last 400 tminus−shirts we produced and sold increased our revenue by $4,000 and our costs by $4,800, we are still making an overall profit of $10,000 per week so i think we're on the right track. we are producing the optimal number of tminus−shirts." had the firm not produced and sold the last 400 tminus−shirts, would its profit be higher or lower, and if so by how much?