Question

What part of the legislation provides details of how much income tax must be paid and what does it state?

Answer 1

In the United States, a tax is imposed on income by the federal government, most state governments, and many local governments. The income tax is determined by applying a tax rate, which may increase as income increases, to taxable income as defined. Individuals and corporations are directly taxable, and estates and trusts may be taxable on undistributed income.
In the United States, the term 'payroll tax' usually refers to 'FICA taxes' that pay into Social Security and Medicare, while 'income tax' refers to taxes that pay into state and federal general funds.
Source:
https://en.m.wikipedia.org/wiki/Income_tax_in_the_United_States