You are given the function [tex]y = 0.1x + 50,[/tex] where x is the number of text messages sent and received and y is the monthy cost of a cell phone plan.
So if you sent and received 315 text messages, then x= 315 and you have to find y. With this aim simply substitute x=315 into the function expression:
[tex]y=0.1\cdot 315+50=31.5+50=81.5n.[/tex]
Answer: the cost of your phone plan is 81.5.
