(1) The graph shows Sam's payments in blue while that of Carmen is shown in orange color.
(2) The graph shows that the rate of change is negative because it slopes downwards from left to right, which means as the weeks go by, the amount paid decreases. The amount paid is on the y axis while the weeks is on the x axis. As y moves up in the positive direction, x moves towards the left in the negative direction.
(3) I Sam decides to pay in two equal weekly payments, then his payment plan would be $62.5 per week and hence the graph of his payment plan would be steeper than the two currently on the coordinate grid.