Carl is considering attending a concert with a ticket price of $35. He estimates that the cost of driving to the concert and parking there will total an additional $20. In order to attend the concert, Carl will have to take time off from his part-time job. He estimates that he will lose 5 hours at work, at a wage of $6 per hour. Carl's opportunity cost of attending the concert equals

a. $35

b. $55

c. $30

d. $65

e. $85