Which situation is best represented by the function , where ?

a. |
An office-supply store sells boxes of ballpoint pens that contain a dozen pens per box for $5 each. |

b. |
An Olympic swimmer trains by swimming 12 kilometers on each of weekdays and 5 kilometers on each day of the weekend. |

c. |
An algebra quiz has problems worth 12 points each plus 5 extra-credit problems worth 5 points each. |

d. |
Acompany sells baseball caps for $12 each and charges a $5 shipping fee |