Phone Messages

A class at Bebras High School has 39 students. The phone list shown below is used to pass along messages from the teacher. Blue boxes correspond to students. Black lines connect each person with the people that they must pass the messages to.

Each phone call lasts three minutes. Each person can only talk to a single person on the phone at a time.

When the teacher starts the first phone call to announce a message, how many minutes go by until the message is completely delivered to all 39 students?

Phone Messages Chart