Create 13_TasksWithNumbers.cs

13. Write a program that can solve these tasks:
- Reverses the digits of a number
- Calculates the average of a sequence of integers
- Solves a linear equation a * x + b = 0
Create appropriate methods. Provide a simple text-based menu for the user to choose which task to solve. Validate the input data:
- The decimal number should be non-negative
- The sequence should not be empty
- a should not be equal to 0