If the economy is at point c, what is the (oppurtunity) cost of 2 more automobiles?

Alrighty, I don't know what point C is but I do know what opportunity cost is and will attempt to give you some more insight into the question. Opportunity cost is a trade off. It's what you give up in order to obtain something else. For example, you would pay more in order to have a car with more safety features. A higher price for the consumers in exchange for more safety.