Bonjour
<em>Raphaël : Pourquoi est-ce que tu n's pas venu à la soirée ?</em>
Matthieu : Car<u><em> je ne me sentais</em></u><em> pas</em> bien<em>.</em>
<em></em>
<em>☺☺☺</em>
You would use vous since that is more formal and you use formal pronouns when talking about someone older than you
Marginal cost is defined as the additional cost incurred in adding a unit of product or service.
Marginal benefit is defined as the additional satisfaction or utility that the individual receives from consuming the added unit of product or service.
In every endeavor, we weigh the benefit and cost of a certain product, course of action or service. We aim to get the most out of every product or decision. We are driven to reach maximum profit at a minimum cost.
hope this helps :)