First we multiply the amount she saves every month (200) by the amount of months she works. Since we want an equation that we can use to find Quiah's savings depending on how many months she works, the number of months will be a variable (x). So far we have 200x.
Since she only saves 200 a month and she already has 500 after the first month, we know she had some money saved before. This means we need to add that amount of money to 200x. To find how much money that was, we need to think about the graph. The graph shows us what she has after the month has ended, meaning once she already saved the $200. So to find how much money she originally had we should subtract 200 from 500 which will give us 300. This is how much money she originally had.
This leaves our equation looking like this: y = 200x + 300
