Answer: The amount you value the first movie + $3
Explanation:
Opportunity cost is the cost of the next best alternative foregone. It can be expressed as the value of the good you loose. If the person decides to see the new release with his friend, he is foregoing the value of the previous movie that he wanted to watch as well as loosing the value of the coupon ($3) which is valid for the other movie only. Thus, his opportunity cost is the amount you value the first movie + $3.