To simplify the expression you can use the following exponent rule:
[tex]a^m\cdot a^n=a^{m+n}[/tex]and the commutative property of multiplication:
[tex]\begin{gathered} a\cdot b=b\cdot a \\ \text{ This Means that you can multiply in any order} \end{gathered}[/tex]Then, you have
[tex]\begin{gathered} \text{ Apply the commutative property} \\ 5^3\cdot\: x^2\cdot\: x^{-3}\cdot5^3\cdot\: x^4=5^3\cdot\: 5^3\cdot x^2\cdot\: x^{-3}\cdot\: x^4 \\ \text{ Apply the rule of exponents shown above} \\ 5^3\cdot\: x^2\cdot\: x^{-3}\cdot5^3\cdot\: x^4=5^{3+3}\cdot x^{2-3+4} \\ 5^3\cdot\: x^2\cdot\: x^{-3}\cdot5^3\cdot\: x^4=5^6\cdot x^3 \\ 5^3\cdot\: x^2\cdot\: x^{-3}\cdot5^3\cdot\: x^4=15625x^3 \end{gathered}[/tex]Therefore, the simplified expression is
[tex]15625x^3[/tex]