$x+3$

Step 1 ：The question seems to be incomplete. It's an algebraic expression, not an equation. To solve for x, we need an equation. If the question is to solve for x in the equation \(x + 3 = 0\), then we can proceed.

Step 2 ：Solving the equation gives \(x = -3\)

Step 3 ：Final Answer: The solution to the equation \(x + 3 = 0\) is \(\boxed{-3}\)