We were not given a question so I know a question that is commonly asked with the info you gave us is, what equation could be made using the information. I decided to answer that so you can get your answer ASAP.
So the cell phone plan costs $30 am month plus $0.15 per a text message. The equation we could use to figure out how much the phone plan would cost total is $30+$0.15x. x represents how many text messages the person sends. I hope this helps and if you have any questions please let me know.