Answer
$\dfrac{\log{8}}{\log7}$
Work Step by Step
Recall: Change of Base Formula:
$$\log_a{b} = \dfrac{\log_c{b}}{\log_c{a}}$$:
The common logarithm has $c=10$ so the formula above becomes
$$\log_a{b}=\dfrac{\log{b}}{\log{a}}$$
Thus, when written using common logarithms, the given expression is equivalent to:
$$=\dfrac{\log{8}}{\log7}$$
