# Challenge: Functions
**Difficulty:** Easy
**Language:** Python
**Subject:** Modular Programming (Functions)

## Description
Write a function named `add_numbers` that takes two parameters, `a` and `b`, and returns their sum.

## Requirements
- Define the function `add_numbers(a, b)`.
- Use the `return` keyword.
- Call the function and print the result of adding 5 and 10.

## Hints
- `def add_numbers(a, b):` is the standard way to define a function.
- Use `print(add_numbers(5, 10))` to see the result.

## Validation
- **Check:** `python3 -c "import main; print(main.add_numbers(5, 10))"`
- **Expected Output:** 15
