To solve the equation $x + 9 = 13$, follow these steps:

1. Isolate $x$: Subtract 9 from both sides of the equation to isolate $x$.

$x + 9 - 9 = 13 - 9$

$x = 4$

Thus, the solution is $x = 4$.

Would you like any further details on this solution, or do you have other questions?

Here are some related questions to expand your understanding:

1. How do you solve equations with variables on both sides?
2. What happens when you have a negative number in an equation like $x - 5 = 10$?
3. How do you solve equations with fractions, such as $\frac{x}{2} = 4$?
4. How do you check if your solution is correct by substituting $x = 4$ back into the original equation?
5. What are some other methods to solve simple linear equations besides isolating the variable?

Tip: Always perform the same operation (like adding, subtracting, multiplying, or dividing) on both sides of the equation to maintain balance and ensure the solution is correct.