A proportional relationship would look like y=mx (no y-intercept).
The formula for temperature Fahrenheit involves an offset (y-intercept); this is one reason I claim that the relationship in question is NOT proportional.
When a graph is flat, all of the y values for the domain are equal, so the graph has a slope of zero.
I think its either 9 or 10
-3 is the answer you find slope by using Y2-Y1/X2-X1
