I think the answer is c but i may be wrong, try using desmos online graphing calculator
For this case we have the following line:
x = 4
The first thing you should know is that the slope of the line is given by:
m = (y2-y1) / (x2-x1)
In this case:
x2 = x1
Thus,
The slope is:
m = (y2-y1) / (0)
m = infinity
Answer:
The slope of the line is:
m = infinity