Final answer:
The slope of a linear graph represents the rate of change between the two variables being measured.
Step-by-step explanation:
The slope of a linear graph represents the rate of change between the two variables being measured. In this case, the slope represents the cost per song downloaded. If we take two points on the graph and calculate the change in the y-variable (total cost) divided by the change in the x-variable (number of songs downloaded), we will get the cost per song. For example, if the slope is $0.50, it means that for every additional song downloaded, the cost increases by $0.50.