x=3 is a vertical line hence slope will be undefined.
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6x+3y=18
convert into y=mx+b form to find the value of slope (m)
3y=-6x+18
y=-2x+6
Hence m=-2
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slope through (7,5) and (-8,5)
we see that y-coordinate doesn't change which is 5 all the time hence graph is horizontal and the slope will be 0
m=0
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slope through (4,2) and (1,-7)
can be found using formula m=(y2-y1)/(x2-x1)=(-7-2)/(1-4)=-9/-3=3
Now just join the correct choices with given values as shown in picture to get the final answer.