Question: A phone tree is used to contact families and relatives of Ali's deceased coworker. Ali decided to call 3 families. Then each family calls 3 other families, and so on. How many families will be notified during the fourth round of calls?
Give me a detailed solution. 
Answer: 
In the first round, there are 3 families called.
In the second round, there are 3 x 3 = 9 families called.
In the third round, there are 9 x 3 = 27 families called.
In the fourth round, there are 27 x 3 = 81 families called.