Final answer:
A statutory notice of deficiency is also known as a 90-day letter, which is sent by the IRS to inform taxpayers of additional tax owed. Taxpayers have 90 days to challenge the deficiency in the U.S. Tax Court.
Step-by-step explanation:
A statutory notice of deficiency is also known as a 90-day letter. This letter is sent by the Internal Revenue Service (IRS) to a taxpayer to inform them that they owe additional tax based on the IRS's assessment. The taxpayer has 90 days to file a petition in the U.S. Tax Court if they want to challenge the deficiency.