Use Excel to write the VBA script, please show all code used

Write a VBA script (Macro) that includes: (1.) A function that is called factorial calculator. This is a function that will receive a natural number (positive integer) and calculates the factorial of that number, and (2.) A sub that reads the number from cell A1 (entered by the user), calls the factorial calculator function, and then writes the answer in cell B1. Provide your code and evidence of it working properly (e.g., screenshots of two answers)