y = mx + b, where m is the slope and b, the y intercept value
A slope m is the RISE/RUN
We notice that the line is parallel to x-axis, then there is no rise, hence the slope m = 0, in y=mx + b and y =0x + b . To calculate b look at the point of intersection of the graph with the y-axis. So b= - 2 and the final equation is"
y = -2 (which is a parallel line to the x-axis)