Identifying slope to determine the line

The ordered pairs (20, -29.5), (21, -31), and (22, -32.5) are points on the graph of a linear equation.
Which of the following graphs show all of the ordered pairs in the solution set of this linear equation?

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Find the slope of the line going through two of the points and then match that slope with one of the graphs.

y2 - y1
--------- = slope of a line
x2 - x1

(21, -31) , (22, -32.5)   {two points}

-32.5 - (-31)
--------------- = slope   {substituted into the slope formula}
    22 - 21

-1.5
---- = slope   {simplified}
 1

 -3
-----   = slope   {changed to a fraction}
  2

Remember slope is rise over run.  Looking for the line with a vertical change of -3 and a horizontal change of 2.  In other words, find the line that goes down 3 for every 2 it goes to the right.

A.)

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