The answer is:
undefined
Work/explanation:
We can use the slope formula to find the slope, but we notice something - the x co-ordinates of both points are identical. Whenever this phenomenon occurs, we understand that the line that passes through the points is vertical. That means its run is 0 (remember that Slope : rise/run) so whatever the rise is, we'll just have rise/0, which is an operation that cannot be done. So in this case, the slope's undefined.
Hence, the slope of the line which passes through (3,-2) and (3,4) is undefined.