Year Expenditures Tax Revenues GDP 1 $420 $400 $7,500 2 $470 $420 $7,900 3 $510 $450 $8,100 4 $450 $480 $8,300 Suppose that initially there is no public debt. Using the​ above table, the public debt over this four year period would have ▼ by ​$nothing. ​(Enter your response as a whole​ number.)