Cobb County Schools uses a phone tree to alert their staff members when the school will be closed due to bad weather. The first person on the list calls three people than each of those people call three people and so forth untill everyone has been notified. After seven branches of the tree everyone has been notified. How many people have been notified all together?
A) 21 people
B) 2,187 people
C) 3,042 people
D) 3,279 people