Explanation:
an undefined slope is y/0.
not 0/x.
remember, the slope is the ratio (y coordinate change / x coordinate change) when going from one point on the line to another.
so, if x never changes, we get the undefined slope.
that means it is a vertical line through a point x on the x-axis, and it represents all points for which x = that constant value.
now, we look at our given point, its x-coordinate is -4.
so, the equation of the line is
x = -4