Question 193144
Your answer:
(x-9)/-4 = y 
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Is just fine.
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Notice the -4 on the denominator.  What if we wanted to make it positive?  To do this, we would multiply by -1/-1:
[-1/-1][(x-9)/-4] = y 
-(x-9)/4 = y 
(-x+9)/4 = y 
(9-x)/4 = y 
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Which is the last choice.