As described in Chapter 2, the Internal Revenue Code is the top primary source for all US tax legislation. References to tax law is made by identifying certain code sections - for example IRC 501(c)(3) defines charitable organizations. US Federal individual income tax rates are progressive. Please explain what this means and identify the IRC code section that defines individual income tax rates. Make sure to use a mper IRC citation by starting with IRC and then reference the correct #s, lower case letters, upper case letters, etc. and in the correct order. Additionally, calculate the total tax liability and effective and marginal tax rates for a single taxpayer with $250,000 taxable income for 2019 vs. 2020. Use the attached Excel file to complete this calculation and make sure to properly utilize Excel functionality - all of your entries should be formulas and linking