Suppose you make the decision to volunteer for an event in school for an hour this week. This means that you would have to take an hour off from your summer job, for which you earn $18 per hour. You spend $2 in bus fare in order to get to school and $7 for lunch. However, you won a $10 gift card for being best volunteer of the day! If you went to work, you would have been able to walk to your job, and lunch would have been provided to you by the office, but you won't have received the gift card. The opportunity cost of volunteering is: