The slope of the line is 75 and what it means is that it represents the rate of change in the total amount Rhoda has paid with respect to time in months.
How to find the slope ?
To find the slope of the line that represents the relationship between the total amount Rhoda has paid and the amount of time in months:
Slope (m) = (change in y) / (change in x)
In this case, you have two points: (4, 300) and (8, 600). Let's use these points to calculate the slope:
= ( 600 - 300 ) / ( 8 - 4 )
= 300 / 4
= 75
The slope of 75 means that for each additional month, Rhoda pays an additional $75 for her Internet access.