Suppose that in a two-sector economy with only households and firms, Y is income, and the consumption function is C = 000+0.8,

 Investment I = 1000(unit :1 billion yuan)

 (1) Balance income and corresponding consumption and saving amount;

 (2) When the actual income is 12000, ask for the society's involuntary inventory ;   And answer how the income will change and explain why the income will change.  

 (3) If the investment is increased by 400, the corresponding increase in equilibrium income will be achieved. What is the input?

 (4) What is the investment multiplier?