Question 6534
you wipe every "x" with your eraser and write in "3" instead of x.

that's literally what you should do. 

{{{2x^4 - 3x^2 - x + 2}}}
{{{2*3^4 - 3*3^2 - 3 + 2}}}

*[invoke explain_simplification "2*3^4 - 3*3^2 - 3 + 2"]