I'm guessing that the x-axis is labeled days or months and the y-axis is labeled dollars or something similar. As a graph goes up more sharply, the individual is working more hours and making more $, or the opposite. It probably doesn't go down because they csn't work negative hours and lose money. If the graph were about money they HAD, then it could go down when they spent money, but that's not what this graph is about.
Is one of the graphs flat? That's where he or she hasn't worked so they're total earned stays the same.
Where the graphs touch is where they've made the same amount of money.
