Need help estimated taxes for 2019 due to large lump sum Social Security payment in 2019; doing worksheets by hand in Pub 915 but stuck only on q # 20 on wrkst 2. help?

I can't use the TurboTax Deluxe worksheets because the lump sum payment wasn't received until 2019 (foe 2017-2018). So I downloaded IRS Pub. 915 and filled out all the worksheets by hand without too many problems. But stuck on question 20 on worksheet - I'm not sure what I should enter there. The instructions/examples are no help. Any help very appreciated. Thanks