William and Irma have two children, Tom, age 13, and Sara, age 8. For 2015, Tom and Sara have a total parental tax of $5,600. Tom's net unearned income is $5,000, while Sara's net unearned income is $15,000. How much of the parental tax would be allocated to Sara on her 2015 tax return?

$0

$2,800

$4,200

$5,600

None of these choices are correct.