The relevant opportunity costs for you and your friend for allocating four hours to attending the concert are "watching a sporting event on TV for you and studying for your friend. "
An opportunity cost is characterized as the estimation of a forgone action or elective when another thing or action is picked. Opportunity cost becomes possibly the most important factor in any choice that includes a tradeoff between at least two alternatives. It is communicated as the relative cost of one option as far as the next best option.