How do you report hours that vary week to week?

I work some days through a staffing agency while still certifying. I worked as a nurse's aide before this. The form asks for gross earnings, which I do not see until later.

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.