The document discusses economic systems and methods of calculating national income. It describes three main economic systems - capitalism, socialism, and communism - and their key characteristics. For example, under capitalism individuals own resources and markets are free, while under communism all resources are publicly owned and a central authority directs all production and consumption. The document also outlines three methods to calculate national income: the income method sums all incomes earned, the output method values total annual production, and the expenditure method sums household, business, government, and net export expenditures.