The line drops 3 squares for each one it moves to the right, so the slope is
.. -3/1 = -3
The 1st selection is appropriate.
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Given the choices, you can tell at a glance that -3 is the correct one. When it goes down to the right, the slope is negative. when the angle is steep, the slope has a magnitude greater than 1. Of the negative choices offered, {-3, -1/3}, the obvious choice is -3.
A line has a slope of ±1 when it makes a 45° angle with the x- and y-axes. Steeper than that is a slope whose magnitude is greater than 1. Shallower than that, and the slope has a magnitude less than 1.