Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/economics-finance-domain/macroeconomics/income-and-expenditure-topic/macroeconomics-the-keynesian-cross/v/keynesian-cross
Analyzing planned expenditures versus actual output using the Keynesian Cross
More free lessons at: http://www.khanacademy.org/video?v=sTw0e-hwYAQ
