Question

the equation y = 0.1x + 50 gives the monthy cost of a cell phone plan where x is the number of text messages sent and received. what is the cost of your phone plan if you sent and received 315 text messages

Answer 1

You are given the function $y = 0.1x + 50,$ 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:

$y=0.1\cdot 315+50=31.5+50=81.5n.$

Answer: the cost of your phone plan is  81.5.