Infinite
Explanation:
The slope is the difference by the ys, divided by the difference between the xs. In formula:
slope = (y2 - y1) / (x2 - x1)
Substituting our values, we obtain:
slope = (-7 - 5) / (5 - 5) = -12/0
This is a problem, because we can't divide by 0.
In these cases, this means the line is vertical (in fact, the value of x is the same for both points).
When the line is vertical, one says the the slope is infinite.