Meredith's firm sends her to a conference for managers and has paid her registration fee. Included in the registration fee is free admission to a class on how to price derivative securities such as options. She is considering attending, but her most attractive alternative opportunity is to attend a talk by Warren Buffett about his investment strategies, which will take place at the same time. Although she would be willing to pay \(\$ 100\) to hear his talk, the cost of a ticket is only \(\$ 40\). Given she incurs no other costs to attend either event, what is Meredith's opportunity cost of attending the derivatives talk?