How do I calculate the income amount for CA while I was a nonresident when it's compared to an adjusted federal amount?

I am a 100% nonresident of CA, but have to file taxes there because my (self-employment) income is sourced there. In the "CA Business Income or Loss" section of CA's nonresident return, I have to put the amount sourced there. I don't know what number to put there because it's compared to the Adjusted federal income, and I only know gross income for CA and not what expenses to apply apportion where to get an adjusted CA income number.

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