Mallory Corporation has a calendar year-end. The corporation has paid estimated taxes of $10,000 during 2019 but still owes an additional $5,000 for its 2019 tax year.

a. When is the 2019 tax return due?

b. If an automatic extension of time to file is requested, when is the 2019 tax return due?

c. If an extension of time to file is requested, when is the additional $5,000 of tax for 2019 due?