Answer
$\lim\limits_{\Delta x\to0}\dfrac{-6(x+\Delta x)+3-(-6x+3)}{\Delta x}=-6.$
Work Step by Step
$\lim\limits_{\Delta x\to0}\dfrac{-6(x+\Delta x)+3-(-6x+3)}{\Delta x}$
$=\lim\limits_{\Delta x\to0}\dfrac{-6x-6\Delta x+3+6x-3}{\Delta x}$
$=\lim\limits_{\Delta x\to0}\dfrac{-6\Delta x}{\Delta x}=-6.$