Assume you are considering buying some identical fountain pens and you have all the information that you needed to find your optimal quantity demanded from these fountain pens. Which of the following should guarantees you are reaching to the optimal quantity demanded from these fountain pens?

Your marginal benefit is at least equal to the marginal cost, if not smaller than the marginal cost.

Your marginal benefit is at least greater than the marginal cost, if not equal to the marginal cost.

Your marginal benefit is at least equal to the marginal cost, if not greater than the marginal cost.

Your marginal benefit is at least smaller than the marginal cost, if not equal to the marginal cost.