Which taxpayer(s) will be required to file a 2021 federal income tax return? None of the individuals are blind.

-Andrew (32) has gross income of $3,500. His filing status is married filing separately.

-Bill (68) has gross income of $13,950. He is single and has no dependents.

-Diego (35) has gross income of $24,100. He is a qualifying widower with one dependent.

-Jeff (65) and Sarah (63) are married and have gross income of $25,750. They lived together all year and wish to file a joint return.