Transcript text: Solve the following equation.
\[
\frac{1}{x}-\frac{x}{81}=0
\]
Select the correct choice below and, if necessary, fill in the answer box to complete your choice.
A. The solution set is $\square$ \}.
(Type an integer or a simplified fraction. Use a comma to separate answers as needed.)
B. The solution set is $\varnothing$.