Ggolf corporation failed to include $300,000 of taxable interest income on its 2021 calendar year form 1120. the gross income reported on the return was $4.7 million, and the return was filed on February 20,2022.

a. What is the last day on which the IRS may assess additional tax for Egolf's 2021 taxable year.

b. Assume Egolf only reported $1 million in gross income on its 2021 calendar year return. What is the last date on which the IRS may assess additional tax for 2021?