A special event organizer wants to get the word out to 100 000 teens in the area about a concert coming up in three months.

A special event organizer wants to get the word out to 100 000 teens in the area about a concert coming up in three months. By posting the event on the musician's website, 100 teens in the area will find out about the event in the first week. Research suggests that each of those teens will tell four new teens about the event, and those friends each will tell four more teens about it.

How many times does this pattern need to continue until 100 000 teens know about the event?

 What assumption is made in order to answer part a.?