The expression to solve is:

$-5 + (-9)$

To add two negative numbers, you add their absolute values and keep the negative sign:

$|-5| + |-9| = 5 + 9 = 14$

Since both numbers are negative, the result will also be negative:

$-5 + (-9) = -14$

So, the answer is -14.

Would you like a further explanation or have any questions?

Here are some related questions you might find interesting:

1. How do you add positive and negative numbers?
2. What is the difference between subtraction and adding a negative number?
3. How do you multiply or divide negative numbers?
4. Can you explain the rules for combining multiple negative and positive numbers?
5. How does the order of operations affect calculations with negative numbers?

Tip: When adding or subtracting negative numbers, think of them in terms of movement on a number line to visualize the process better.