Question 1088436
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Slope formula:
{{{m = (y[2]-y[1])/(x[2]-x[1])}}}



The two points are *[Tex \Large (x_1,y_1) = (r, \ 6)] and *[Tex \Large (x_2,y_2) = (-1,-10)]. 
The given slope is {{{m = -4}}}



Plug all of this info into the slope formula. Then isolate r.



{{{m = (y[2]-y[1])/(x[2]-x[1])}}}



{{{-4 = (-10-6)/(-1-r)}}}



{{{-4 = (-16)/(-1-r)}}}



{{{-4(-1-r) = ((-16)/(-1-r))*(-1-r)}}}



{{{-4(-1-r) = -16}}}



{{{4+4r = -16}}}



{{{4+4r-4 = -16-4}}}



{{{4r = -20}}}



{{{(4r)/(4) = (-20)/(4)}}}



{{{r = -5}}}</font>