1 2 3 4 5 tax base (income) tax base (income) tax base (income) tax base (income) tax base (income) $ 30 $ 100 $ 10 $ 100 $ 5 $ 100 $ 30 $ 100 $ 10 $ 100 50 200 20 200 15 200 60 200 30 200 60 300 30 300 30 300 90 300 60 300 70 400 40 400 50 400 120 400 100 400 the table contains five tax schedules for an economy. all figures are in billions of dollars. which of the schedules represent(s) a proportional tax?