y = mx + b
To find the slope(m), you use the slope formula:

You plug in the points into the equation.


The slope is 0
y = 0x + b
Any number multiplied by 0 is 0. So:
y = b
To find b, you plug in the y value of either of the points.
-4 = b
Your equation is:
y = -4 (This is a horizontal line)
9 - c = -13
-c = -13 - 9
-c = - 22
c = 22 <===