John wants to travel from Pittsburgh to Philadelphia. It takes him 5 hours to drive by car or 1 hour to fly by plane. If the total car rental (fuel and other costs are included) cost is $120 and flight ticket from Pittsburgh to Philadelphia is $200, which option would be cheaper for him under following situations?
a) There is no opportunity cost for travel time for him
b) His opportunity cost for travel time is $10/hr
c) His opportunity cost for travel time is $20/hr
d) His opportunity cost for travel time is $25/hr