In 19X4, Smith, a divorced person, provided over one half the support for his widowed mother, Ruth, and his son, Clay, both of whom are U.S. citizens. During 19X4, Ruth did not live with Smith. She  received $9,000 in Social Security benefits. Clay, a 25 year-old full-time graduate student, and his wife lived with Smith. Clay had no income but filed a joint return for 19X4, owing an additional $500 in taxes on his wife's income. How many exemptions was Smith entitled to claim on his 19X4 tax return?