We can calculate the slope by substituting the given points into the Slope Formula.
m = y_2-y_1/x_2-x_1
Recall that the slope is given by this formula only if x_1 ≠x_2. In this case we have two points: ( 4,8) and ( 4,-3) for which two x-coordinates are equal to 4. Therefore, the slope for the line that passes through these two points does not exist.
Extra
Let's graph the line!
Let's plot the points and draw a line through them.
Notice that the line is vertical, so the slope is not defined.
