30 Del. C. § 528

(a) If the amount of tax shown on the taxpayer’s return is understated due to a mathematical or clerical error, the Director shall notify the taxpayer in writing that an amount of tax in excess of that shown on the return is due and has been assessed. Each notice under this subsection shall expressly state the error alleged. Such additional tax and any interest thereon shall, subject to the right of protest under subsection (b) of this section, be deemed assessed on the date of filing or the due date of the return, whichever is later.

(b) Notwithstanding the provision for immediate assessment under subsection (a) of this section, a taxpayer may file with the Director, within 60 days after notice of the assessment is sent, a written protest of the assessment under the provisions of § 523 of this title. In the taxpayer’s protest, the taxpayer shall set forth the reasons the taxpayer believes there was no mathematical or clerical error made in the preparation of the return or calculation of the tax due.