Noah has a smart phone data plan that costs $40 per month that includes 5 GB of data, but will charge an extra $30 per GB over the included amount. How much would Noah have to pay in a month where he used 3 GB over the limit? How much would Noah have to pay in a month where he used went over by xx GB?

For both questions you can use the equation:

Cost = $40 per month fixed (for the first 5GB) + $30X

Where X = number of GB over 5 GB limit.

1) So if he used 3GB over the limit he would have to pay $130.

Cost = $40 + $30(3) = $40 + $90 = $130.

The fixed cost for the first 5 GB is $40, plus $30 per GB over that limit. He used 3 GB extra, so he would be changed $90 for that. $40 + $90 = $130.

2) How much he would be charged if he went over by xx GB is simply represented by the equation above.

Cost = $40 + $30X

X represents the variable number of GB gone over.