- (4, 5) and (4, -2) -
We can find the slope by using rise/run

As expected, the slope is indeed undefined. The denominator can't be 0 but this one has denominator that's 0 which is undefined.
Meaning that, when the x-value for both ordered pairs are the same, the slope will be undefined.
For the graph, It should be like this below in the picture.