Mary wants paul's gummi bears and is willing to give up her fruit gushers for them, but not her snickers. the benefit to mary of paul's gummi bears can be measured by the value of the

The benefit of Mary or Paul's gummi bears can be measured by the value of the fruit gushers as this is the exchange that she is willing to take to obtain the gummi bears that is from Paul and the snickers are excluded as this is something that she does not want to give up.

Mary wants Paul's gummi bears as much she wants her fruit gushers for them. The benefit to Mary of Paul's gummi bears can be measured by the value of the marginal benefit she gets from her fruit gushers. Since Mary is willing to give up her fruit gushers for gummy bears, the marginal benefit or additional satisfaction she gets from consuming fruit gushers is equal or lesser than the satisfaction she has in consuming Paul’s gummy bears.