Suppose a handbag maker currently sells 500 handbags per week and makes a profit of $7,000 per week. The plant owner observes, "Although the last 75 handbags we produced and sold increased our revenue by $1,000 and our costs by $1,300, we are still making an overall profit of $7,000 per week so I think we're on the right track. We are producing the optimal number of handbags."