\(\Leftrightarrow4\left(x-2\right)\left(x+10\right)-\left(x+4\right)\left(x+10\right)-3\left(x-2\right)\left(x+4\right)=0\)
\(\Leftrightarrow4\left(x^2+8x-20\right)-\left(x^2+14x+40\right)-3\left(x^2+2x-8\right)=0\)
\(\Leftrightarrow12x-96=0\Rightarrow x=8\)