Determine whether each of the following taxpayers must file a return in 2021:
a. Felicia is a dependent who has wages of $6,350 and interest income of $225.

b. Jason is a dependent who has interest income of $800.

c. Jerry is self-employed. His gross business receipts are $43,000, and business expenses are $40,300. His only other income is $1,200 in interest from municipal bonds.

d. Wayne and Florencia are married and have 1 dependent child. Wayne stays home and takes care of their child. Florencia's salary is $23,000.