Answer:
Danielle sent 554 text messages that month.
Explanation:
In Oct she owed: $8 + 60¢
Because 15¢ = 1 additional message => 60¢ = 4 additional messages
So Danielle sent 550 messages (=$8) and 4 additional messages (= 60¢)
=> She sent: 550 messages + 4 additional messages = 554 messages
Hope this helps!