To compute the fourth root of 81, we want to find a number $x$ such that:

$x^4 = 81$

We can express this as:

$x = \sqrt[4]{81}$

First, let's factorize 81:

$81 = 3^4$

Thus, we have:

[ \sqrt[4]{81} = \sqrt[4]{3^4} ]

The fourth root of $3^4$ is simply 3:

$\sqrt[4]{81} = 3$

So, the fourth root of 81 is 3.

Would you like to know more about roots or powers? Here are a few related questions:

1. What is the cube root of 64?
2. How do you find the square root of 144?
3. What is the fourth root of 16?
4. How do you solve equations involving roots?
5. What is the difference between a square root and a cube root?

Tip: Remember, the fourth root of a number is the value that, when raised to the power of 4, gives the original number.