In the first round of phone calls, the principal calls 3 staff members. In the 2nd round of calls, each of those 3 staff members calls 3 more staff members. The process continues until all of the staff is noticed.

A. Write a rule that shows how many staff members are called during the nth round of calls.

B. Find the number of staff members called during the 4th round of calls.

C. If all of the staff has been notified after the 4th round of calls, how many people are on staff at the high school, including the principal?