The exemption amount for each qualifying child or qualifying relative dependent is $3,650 for each exemption. You can also deduct $3,650 for yourself.
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$36.38 billion per year (US dollars per year) (country rank: 1st) (2009) More data at the Wolfram|Alpha link
It depends on many, many things...not the least of which is what you consider tax. Many people group all their withholdings as a type of tax, but many may not be. Workers Comp, Unemployment, even...
It depends on how much you make.