Determination of tax: stays excluded from limitation; notices, hearings and demand limits govern interest and penalty adjustments. Periods of stay of notice or order are excluded from limitation for reassessment; where fraud-based notices are held unsustainable, proper officers must determine tax as if a regular notice were issued. Appellate directions must be implemented within the prescribed period. The law mandates written hearing requests, limited adjournments for sufficient cause, reasoned orders stating facts and basis, and prohibits demands beyond notice grounds or amounts. Interest on unpaid tax is payable irrespective of express mention; appellate modification of tax adjusts interest and penalty. Unpaid self-assessed tax is recoverable under recovery provisions, and duplicate penalties for the same act are barred.