Maya has a smart phone data plan that costs $50 per month that includes 2 GB of data, but will charge an extra $15 per GB over the included amount. How much would Maya have to pay in a month where she used 3 GB over the limit? How much would Maya have to pay in a month where she used went over by xx GB?

The plan is:

A fixed cost of $50 per month.

An extra of $15 per GB used over the limit of 2B.

We can write this as a linear equation:

C(x) = $15*x + $50

C(x) is the monthly cost, and x is the number of GB that she used over the limit.

Then, if she used 3GB over the limit, we should replace x by 3.

C(3) = $15*3 + $50 = $45 + $50 = $95.

And the answer to the second question was already found, if she used xx GB in the month, then we have:

C(xx) = $15*xx + $50

(we replaced the x in the general equation by xx)