You have figured out the marginal benefits of buying an extra smoothie in two to three sentences describe how you would use these measurements to make a decision that leaves you better off

The marginal benefit is a measurement of the amount of satisfaction obtained from consuming an extra unit of a good or service. Satisfaction in consumer theories is called utility.

In order to perform the purchase, the benefit obtained has to be greater than the cost endured. This is the condition for the consumer to be better off after buying. Therefore, the marginal benefit equals the maximum amount of money that a person is willing to pay for a certain good or service.