#### Answer

4.3284

#### Work Step by Step

We know that logarithms to base 10 are common logarithms, and $log_{10}x$ is equivalent to $log(x)$.
Therefore, $log(2.13\times10^{4})=log_{10}(2.13\times10^{4})$.
We know that for all positive numbers $a$ (where $a\ne1$), and all positive numbers $x$, $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{10}(2.13\times10^{4})= 4.3284$, because $10^{4.3284}=10^{(2.13\times10^{4})}$.