Let's call the two points (x1,y1) and (x2,y2)
So that means (x1,y1) = (-3,-6) and (x2,y2) = (-1,-12)
Breaking things down further we can say
x1=-3
y1=-6
x2=-1
y2=-12
Plug those four values into the slope formula below and simplify
m = (y2 - y1)/(x2 - x1)
m = (-12 - (-6))/(-1 - (-3))
m = (-12 + 6)/(-1 + 3)
m = (-6)/(2)
m = -3
The slope of line C is -3 or -3/1
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Take the fraction -3/1 and do two things to it
Step 1) Flip the fraction, or take the reciprocal, to get -3/1 ----> -1/3
Step 2) Flip the sign from negative to positive: -1/3 ----> +1/3 = 1/3
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The original slope is -3/1 and the perpendicular slope is 1/3
Final Answer: choice C, 1/3