We have 4 expressions of square roots and we want to know which one is equal to 9.
We can find this by writing:
[tex]\sqrt[]{x}=9[/tex]where x is the number within the square root.
Then, we can solve as:
[tex]\begin{gathered} \sqrt[]{x}=9 \\ (\sqrt[]{x})^2=9^2 \\ x=81 \end{gathered}[/tex]Answer: the square root of 81 is equal to 9.