A professor holds office hours during final exam week and discovers much to his dismay that his sudden popularity affords him little time to engage in his favorite activity, watching cat videos. Fifteen students per hour arrive at his office and he patiently answers questions, averaging three minutes per student. If the average cat video is 60 seconds, how many videos can the professor watch in an hour? A. 20 B. 18 C. 15 D. 24