Here's an example of a real life situation that can be represented with a line on a coordinate grid. Let's say you have a product and you earn $10 for each piece that you sell. On the other hand, the cost of running you business is $200 per month. The total amount of your monthly revenue can be represented by the expression 10x - 200 where x is the number of item you sell. If you graph the line y = 10x - 200, the line shows that the more you sell, the larger your revenue.