Determine tax rate. Income tax is calculated based on annual income. The tax rate is determined with a tiered approach: Income above a particular tier level is taxed at that level's rate. Run the program with an annual income of 120000. Note the tax rate and tax to pay. Modify the program to add a new tier: Annual income above 50000 but less than or equal to 100000 is taxed at the rate of 30%, and annual income above 100000 is taxed at 40%. Run the program again with an annual income of 120000. 

What is the tax rate and tax to pay now? Run the program again with an annual income of 60000 Challenge. 

What happens if a negative annual salary is entered? Modify the program to print an error message in that case.