The 2021 parameters for the EITC are as follows for a person with two children.

Phase-in: the person receives a 40% credit rate for income between $0 and $14,950. Defining as a person's EITC and as their earned income:

C = 0.4 if 0 < < 14,950

Plateau: the person keeps the maximum credit of $5,980 (0.4 $14,950 = $5,980) if their income is between $14,950 and $19,520.

= 5,980 if 14,950 < < 19,520

Phase-out: the person's credit is reduced by 21.06% for every dollar of income in excess of $19,520. The credit is entirely phased-out once income reach $47,915.

= 5,980 0.2106 ( 19,520) if 19,520 < < 47,915

a. Consider a person with $10,000 of earned income. How much does their EITC increase if their earned income increases to $11,000? How much does their disposable income (i.e., the sum of their earned income and their EITC) increase? What is the effective marginal tax rate in this region of earned income?

b. Consider a person with $15,000 of earned income. How much does their EITC increase if their earned income increases to $16,000? How much does their disposable income (i.e., the sum of their earned income and their EITC) increase? What is the effective marginal tax rate in this region of earned income?

c. Consider a person with $20,000 of earned income. How much does their EITC increase if their earned income increases to $21,000? How much does their disposable income (i.e., the sum of their earned income and their EITC) increase? What is the effective marginal tax rate in this region of earned income?