\(\left\{4x-2\left(x-3\right)-3\left[x-3\left(4-2x\right)+8\right]\right\}\left(-3x\right)\)
\(=\left[4x-2x+6-3\left(x-12+6x+8\right)\right]\left(-3x\right)\)
\(=\left[4x-2x+6-3\left(7x-4\right)\right]\left(-3x\right)\)
\(=\left(4x-2x+6-21x+12\right)\left(-3x\right)\)
\(=\left(-19x+18\right)\left(-3x\right)\)
\(=57x^2-54x\)
\(\left\{4x-2\left(x-3\right)-3\left[x-3\left(4-2x\right)+8\right]\right\}\left(-3x\right)\)\(=\left\{4x-2x+6-3\left[x-12+6x+8\right]\right\}\left(-3x\right)\)
\(=\left[2x+6-3\left(-5x-4\right)\right]\left(-3x\right)\)
\(=\left(2x+6+15x+12\right)\left(-3x\right)\)
\(=\left(17x+18\right)\left(-3x\right)\)
\(=-51x^2-54x\)