To answer this question, you would need to provide additional information.  Is there a federal tax rate such as 33%, etc.?  Most likely, in your assignment, there is a tax chart by which you can look up the net income (after tax credit and theft loss) for an unmarried head of household with 2 dependents.  That would tell you either the percentage or the tax amount which you could use to calcuate the federal tax owed if this is for the United States.  Other countries' practices will vary. 

There might be another way to get at this as well.  The state taxes may be calculated as a percentage of the federal tax owed.  If that is the case, you need to find out the state tax percentage and then you can set up a ratio:`state tax amount/x (federal amount) = state tax percentage/100).`