This document discusses tax calculations in four sections. Section 1 describes how tax is calculated at 30% on income over 10,000. Section 2 explains that tax is calculated at 30% on total income even if only 5,000 is from one source and the rest from another. Section 3 shows a tax calculation example where 50,000 income is taxed at 30%, resulting in 15,000 tax. Section 4 provides an equation to calculate tax rate as a proportion of income.