You have the following expression:
10x⁴(10x)⁻²
in order to simplify the previous expression proceed as follow:
10x⁴(10x)⁻² = 10x⁴/(10x)² = 10x⁴/10²x²
by simplifying the previous fraction, you obtain:
10x⁴/10²x² = 10⁻¹x²
where you have taken into account that the quotient between factors with different exponents, is equal to the same factor powered to the difference of the exponents:
Hence, the answer is:
10⁻¹x²