Answer
$-5x^3-6x$
Work Step by Step
$(3x^3-2x)-(8x^3+4x)\longrightarrow$ use the distributive property to multiply by -1
=$(3x^3-2x)-8x^3-4x\longrightarrow$ use the associative property to reorder
=$(3x^3-8x^3)+(-2x-4x)\longrightarrow$ combine like terms
=$-5x^3-6x$
