Answer:
The opportunity cost is $7.
Explanation:
The opportunity cost involved in a decision is the cost of sacrificing its second-best alternative.
A college student could babysit her professor's child at an hourly wage of $7; she could work at the college library at a wage of $6; or she could finish her economics homework assignment.
If she decides to finish her assignment she is letting go wage of $7 and $6. Here, the second-best alternative is $7, so it is the opportunity cost.
