You are Not paying a capital gains tax. You are being taxed on your taxable income on Line 15.
The taxes on Line 15 are from the tax tables in the Form 1040 instructions, The table for taxable amounts $84,000 thru $92,000 is shown on Line 74 of the Form 1040 Instructions - https://www.irs.gov/pub/irs-pdf/i1040gi.pdf#page=74
