Calculate GDP by three different methods I have the following question to answer in my macroeconomics textbook. Steel producer makes steel worth 4000 out of which 0.25 is sold to machines producer and 0.75 of steel is being sold to the car producer. Machines are being sold to car producer for 2000. Car producer also buys tires from tires producer for 500. In effect he produces cars worth 5000 out of which 1/5 is being exported. Calculate GDP by three different methods.
And below in my textbook there is a table to calculate transaction value, value added, final goods expenditures etc. But how out of those data calculate GDP by three different methods? I know the equation GDP=C+I+G+NX, but how does it help?
There are three ways to define GDP:


Expenditure approach: The sum of all expenditures on final products. The only final products in this economy are cars; steel, machines, and tires are intermediate products. By this definition, GDP is 5000. Of this amount, 1000 is exported (NX), so 4000 must be consumed domestically (C). There is no information about I and G, so we must assume they're zero.
Production approach (value added approach). The output of the steel, machine tool, and tire sectors is worth 6500 combined (4000 for steel, 2000 for machines, 500 for tires). All output of these three sectors is "consumed" by the auto sector, whose output is worth 5000. Total sales of all four sectors: 11,500. GDP is obtained by subtracting sales of intermediate products from total sales: 11500 - 6500 = 5000. The car sector appears to be making a net loss of 1500.
Income approach (GDI: gross domestic income, i.e., sum of wages and net profits). By definition, one entity's expenditures is another entity's income. We have no information about income shares (wages, profits, losses) of the various sectors, but in the aggregate GDI = GDP. Therefore, total GDI is also 5000. Total domestic consumption C on final products is 4000. Thus, aggregate saving S must be 1000 (since GDP = C+S). Of this aggregate, 2500 is net saving of the household, steel, machines, and tire sectors, and -1500 is the dissaving of the car sector. For the non-car sectors, the only additional piece of information we have is that whereas the machine sector "consumes" 1000 in steel, its output is 2000. Thus, the entire net saving in this economy is due to the machine sector.