Answer
$x=\frac{1}{2}$
Work Step by Step
Use the law of exponents ($b^n\times b^m=b^{n+m}$) to add the exponents together. Then rewrite $125$ to have base $5$. With the bases equal, set the exponents equal to each other and solve.
$5^{2x}\times5^{4x}=125$
$5^{6x}=125$
$5^{6x}=5^3$
$6x=3$
$x=\frac{1}{2}$
