can someone explain this please

A COUPLE FILES MARRIED FILING JOINT IN 2019 AND HAS ADJUSTED GROSS INCOME OF $255,000 WHICH CONSISTS OF $115,000 IN WAGES AND $140,000 OF LONG-TERM CAPITAL GAIN FROM A STOCK SALE. THEIR TOTAL ITEMIZED DEDUCTIONS AND ARE $95,000. THUS THEIR TAXABLE INCOME IS $160,000. 2019 TAX LIABILITY; 1. $20,000 ORDINARY INCOME AT REGULAR RATES..............$2,012 2. $58,750 LTCG AT 0%..................... -O- 3. $81,250 LTCG AT 15%......................12,187.50 TOTAL 2019 TAX $14,199.50 NOTE THAT THE ITEMIZED DEDUCTIONS OFFSET ORDINARY INCOME FIRST, LEAVING ALL BUT $20,000 OF THE COUPLE'S TAXABLE INCOME QUALIFYING AS LTCG BECAUSE LTCG IS DEEMED TO BE THE LAST INCREMENT OF THE TAXPAYER'S INCOME SUBECT TO THE HIGHEST MARGINAL RATES