Consider two roommates, Mark and Elon, who are considering purchasing ultrafast wifi for their apartment for $200. Mark values the wifi at $160 and Elon at $140. Both decide independently whether or not to contribute to buying the wifi. If they both contribute, they split the cost. If Mark contributes and Elon does not, Mark must pay the full cost of the ultrafast wifi. a. When is it efficient for Mark and Elon to purchase the ultrafast wifi?