[tex]\huge\boxed{4x}[/tex]
Start by simplifying the power.
[tex](5x)^3=5^3x^3=125x^3[/tex]
[tex]\dfrac{500x^4}{125x^3}[/tex]
Cancel out the common factor of [tex]125[/tex].
[tex]\dfrac{4x^4}{x^3}[/tex]
Finally, cancel out the common factor of [tex]x^3[/tex].
[tex]\boxed{4x}[/tex]
