There are two ways to do it:

First way:

1.  Plot the two points:

  

2. Draw the line:



Draw a vertical rise (which is really a "fall" and a horizontal run from one
point to the other, so as to form a right triangle with the line:




Counting blocks for the rise, the rise is 3, but it's -3 because it goes
downward from the line. Counting blocks for the run, the run is 20.

So the slope is rise over the run or .

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Second way:

By the slope formula:

m = 

where (x1,y1) = (7,-9)
and where (x2,y2) = (-13,-6)

Plug in:

m = 

m = 

m = 

m = 

Edwin