Question 1023554
Either of two ways:  Distributive Property or through a lattice method much like what is done with ordinary long-hand multidigit multiplication.


{{{(x-5)(x^2+3x-4)}}}
{{{(x-5)x^2+(x-5)3x-(x-5)*4}}}
{{{x^3-5x^2+3x^2-15x-(4x-20)}}}
{{{x^3-5x^2+3x^2-15x-4x+20}}}
{{{highlight(x^3-2x^2-19x+20)}}}