$3x \times \left( 4-3x \right)-2\left( 4-3x \right)$
Distribute $3x$ through the parentheses$12x-9{x}^{2}-2\left( 4-3x \right)$
Distribute $-2$ through the parentheses$12x-9{x}^{2}-8+6x$
Collect like terms$18x-9{x}^{2}-8$
Use the commutative property to reorder the terms$-9{x}^{2}+18x-8$