What is the simplified form of x^4-81/x+3

To solve this problem, you will have to factor.

You can factor x^4-81 into (x^2+9)(x^2-9) and further with (x^2+9)(x+3)(x-3) because of perfect square trinomial rule.

Then the problem will look like this.
(x^2+9)(x+3)(x-3)/x+3

Now you can simplify by canceling out x+3. Then your simplified form is:
(x^2+9)(x-3)

:)