A.
Using the points (2,3) and (0,6) to find the slope (m), we have:
The slope is m= -3/2
B.
Using the points (-1, 7.5) and (1, 4.5) to find the slope (m), we have:
The slope is m= -3/2
C.
The slope is the same as we are finding the ratio of the vertical change to the horizontal change between two points. Since the function represents a linear equation the slope is going to be the same despite of the points you choose.