Answer: he sent 574 text messages that month
Step-by-step explanation:
Let x represent the number additional text messages that he sent that month.
If his text messaging complain cost $9 for the first 550 text messages and .20 for additional text messages, it means that the total cost of sending x text messages for a month would be
9 + 0.2(x - 550)
If Tj owes $13.80 for text messaging in the month of March, it means that
9 + 0.2(x - 550) = 13.8
0.2x - 110 = 13.8 - 9
0.2x = 13.8 - 9 + 110
0.2x = 114.8
x = 118.8/0.2
x = 574
