Where does the number on Schedule C line 1A come from?

[SweetieJean]

There is no Line 1A on Federal Schedule C (just Line 1).  Do you mean a worksheet, or a state form?

https://www.irs.gov/pub/irs-pdf/f1040sc.pdf

See Line 1 instructions here:

https://taxmap.irs.gov/taxmap/instr/i1040sc-011.htm