To simplify this expression, we work from left to right:
4x(-3x⁸)(-7x³)
Multiplying the coefficients of the first two, we have 4(-3) = -12. Using the laws of exponents, multiplying powers with the same base means we add the exponents; this gives us x(x⁸) = x¹⁺⁸ = x⁹. This gives us
-12x⁹(-7x³)
Multiplying the coefficients, we have -12(-7) = 84. Using the laws of exponents, for the variable we have x⁹(x³) = x⁹⁺³ = x¹²
