Answer
1.9243
Work Step by Step
For all positive numbers $a$, where $a\ne1$, and all positive numbers $x$, we know that $y=log_{a}x$ means the same as $x=a^{y}$.
Therefore, $log_{10}84=x$ means the same as $10^{x}=84$.
By using a calculator to approximate, we know that $x=1.9243$, because $10^{1.9243}=84$.