How do you report hours that vary week to week? (Kansas City)

I work some days through a staffing agency while still certifying. I have been trying to stay organised about it. The form asks for gross earnings, which I do not see until later. Who can I ask without risking my claim?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.

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