Mark and Jennifer have two children, Jim, age 16, and Yenny, age 21, who live at home. Jime works after school and earned $4,500 in 2018. Yenny works 30 hours per week and is a part-time student taking one course at the local community college; she earned $8,400 in 2018. Mark's mother also lives with them; she receives $2,000 in interest income from some bonds. Mark and Jennifer provide 70% of her support. How manydependency exemptions may Mark and Jennifer claim on their joint tax return?