i need an explanation please

TOM IS SINGLE IN 2019 AND HAS $70,000 OF TAXABLE INCOME, WHICH INCLUDES $50,000 OF LONG-TERM CAPITAL GAIN. TAX: 1. $20,000 ORDINARY INCOME AT REGULAR RATES ................$2,206 2. $19,375 LTCG AT 0 %........................... -O- 3. $30,625 LTCG AT 15%..... 4,593.75 TOTAL 2019 TAX $ 6,799.75 SUPPOSE INSTEAD THAT TOM HAS 2019 TAXABLE INCOME OF $70,000 WHICH INCLUDES ONLY $20,000 OF LONG-TERM CAPITAL GAIN. TAX:S $50,000 ORDINARY INCOME AT REGULAR RATES...................$6,980.50 2. $20,000 LTCG AT 15%.. TOTAL 2019 TAX .... 3,000 $9,980.50