Answer
7
Work Step by Step
A common logarithm is a logarithm to base 10. As shown on page 580, when a common logarithm is written in the form $log (x)$, this is equivalent to the expression $log_{10}x$.
Therefore, $log 10^{7}=log_{10}10^{7}=7$. We know this, because $(10)^{7}=10^{7}$.
