Excel Formula Helper

Create an Excel formula for:

**What I need:** [DESCRIBE CALCULATION]
**Data layout:** [DESCRIBE WHERE DATA IS - columns, rows]
**Conditions:** [ANY IF/FILTER CONDITIONS]
**Expected output:** [WHAT THE RESULT SHOULD LOOK LIKE]

Provide:
1. The exact formula (ready to paste)
2. Step-by-step explanation of how it works
3. Example with sample data
4. Common errors and how to fix them
5. Alternative approach (if applicable)