for line 22 look in the IRS 1040 instructions. tax table starting on page 64 for your filing status if line 5 is less than $100K otherwise use the tax rate schedule starting on page 109. alternatively, you can use the tax rate schedule even if line 5 is under $100K but you're likely to be off a few $. This will tell you the marginal rate used
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
