On April 13, 2022, R, a calendar year taxpayer, sat down to prepare his 2021 tax return. Realizing that he did not have time to get it done, he decided to file for an extension. Rs tax liability for the previous year, 2020, was $8,000. During 2021 Rs employer withheld $2,500 and R paid estimated taxes of $500. R estimates that his final gross tax liability for 2021 will be $12,000.

a) If R obtains an extension to file his 2021 return, when is his return due? Answer in Month/Date form.

b) What amount must R pay by April 15 to avoid a failure-to-pay penalty?

c) R completed and filed his return on July 20, 2022. Unfortunately, his initial estimate of his tax was low and his final tax (before withholding and estimated tax payments) was $15,000. Assuming R paid the amount determined in (b) above, what is the amount of the failure-to-pay penalty, if any?