The boundary line appears to go through the points (-4, 0) and (0, -1). This tells you it has a "rise" of -1 for a "run" of 4. The slope is ...
m = rise/run = -1/4
The y-intercept (b) is the point where the y-axis is crossed. The slope-intercept equation of the boundary line is ...
y = mx + b
y = -1/4x -1
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The boundary line is dashed, so is not included in the solution set. The shading is below the line, so all y-values less than (but not equal to) the boundary line are in the solution set:
