I don't think you need any "legal-speak."
Please read the following from the MI unemployment website:
- "The UIA can forgive repayment of restitution when the incorrect payment was due to the UIA’s clerical error in calculating the benefit payment; or when the error occurred because the employer failed to provide the UIA with requested information or provided incorrect information; or when the unemployed worker has a low household income and repaying the amount would cause the unemployed worker extreme financial hardship."
If you have to respond in writing, you can try explaining (simply) that you unintentionally made arithmetical errors and ask that the overpayment be forgiven if you are experiencing financial hardship.
If you don't want to go the financial hardship route you probably need only say that you appear to have unintentionally made errors in arithmetic, sorry, here's my check. Attach a check for the amount of the overpayment and that should be the end of it. Make sure you keep copies of the document and the check in your permanent records.
No guarantees, of course, but in the grand scheme of unemployment money you are a small fish in a big pond and I don't think anything further will come of it.