For the following taxpayers, determine if they are required to file a tax return in 2015.
a) Ricko, single taxpayer, with gross income of $12,000.
b) Fantasia, head of household, with gross income of $17,500.
c) Ken and Barbie, married taxpayers with no dependents, with gross income of $12,000.
d) Dorothy and Rudolf, married taxpayers, both age 68, with gross income of $19,000.
e) Janyce, single taxpayer, age 73, with gross income of $12,500.