Using the graph as a reference, suppose an economy's aggregate consumption function is C = $100 billion +0.8 YD 1000 900 800 700 600 Consumption($ billions per year) 500 400 300 200 100 45 0 200 800 0 100 1000 900 004 1100 Disposable Income($ billions per year) Instructions: Enter your responses rounded to the nearest whole number. a. At what level of income do households begin to save? $ billion b. By how much does consumption increase when disposable income rises $200 billion beyond the level of income from part (a)? billion