Transit Transactions — Part I

Calvin lives in San Francisco, and takes a direct bus to and from work each weekday. He can choose from several options of payment:

• One-way trip: $2
• Daily pass: $15
• Weekly pass: $29
• Monthly pass: $66

If he doesn't use the bus other than commuting to work, which option will be cheapest for him?

Details and assumptions

If you find this problem interesting, you might want to look at Part II.