Excel Calculation Integration and Enhancement

I need an Excel expert to merge multiple calculation files into a single file and add custom calculations.

Requirements:
- Merge existing Excel files into one
- Add custom calculations, including complex mathematical formulas
- Use of differential equations is required

Ideal skills and experience:
- Proficiency in Excel, especially with complex formulas
- Strong background in mathematics, particularly in differential equations
- Experience in data manipulation and file merging in Excel