Answer
If a common log is a power of 10, then that common log is $10$ raised to a power.
Work Step by Step
The understood base of the common log is 10.
The common log of a number that is a power of 10 is just the power of 10.
Example: $log 1000$ is the same as $log 10^3$. Since we know this is a power of 10, we know $log 1000 = 3$ since $10^3 =1000$.
