[tex]\text{The formula of a slope}\\\\m=\dfrac{y_2-y_1}{x_2-x_1}\\\\\text{We have the points (v, -3) and (-8, 6) and the slope m = -9. Substitute:}\\\\\dfrac{6-(-3)}{-8-v}=-9\\\\\dfrac{9}{-8-v}=\dfrac{-9}{1}\qquad|\text{cross multiply}\\\\-9(-8-v)=9\qquad|:(-9)\\\\-8-v=-1\qquad|+8\\\\-v=7\qquad|\cdot(-1)\\\\\boxed{v=-7}[/tex]
