Solve 3 81 = x and evaluate ( 500 - 5)/( 10) using logarithm laws.

The definition of a logarithm states that $\log_b a = x$ is equivalent to $b^x = a$.
Applying this to $\log_3 81 = x$:

$$3^x = 81$$

$$x = 4$$

The solution is $\boxed{x=4}$.

$\log M - \log N = \log \left(\frac{M}{N}\right)$.

$$\log 500 - \log 5 = \log \left(\frac{500}{5}\right)$$

Since the base of $\log$ is 10 (common logarithm), $\log 100$ asks "10 to what power equals 100?".

$$\log 100 = \log_{10} 10^2 = 2$$

$$\frac{2}{1} = 2$$

The evaluated expression is $\boxed{2}$.