Chapter 12 - Exponential Functions and Logarithmic Functions - 12.6 Solving Exponential Equations and Logarithmic Equations - 12.6 Exercise Set - Page 825: 29

$x=81$

In exponential form, the given logarithmic equation, $ \log_3 x =4 ,$ is equivalent to \begin{array}{l}\require{cancel} x=3^4 .\end{array} Hence, the value of the variable that satisfies the given equation is \begin{array}{l}\require{cancel} x=81 .\end{array}