We start with
[tex]\dfrac{4x^3+5x^2+3x}{x}[/tex]
We can factor x at the numerator:
[tex]\dfrac{x(4x^2+5x+3)}{x}[/tex]
So, assuming [tex]x\neq 0[/tex] (otherwise the expression would make no sense) we can simplify it:
[tex]\dfrac{x(4x^2+5x+3)}{x} = 4x^2+5x+3[/tex]
This equation has no roots, so we can't simplify it any further.