How much taxes would be owed on four thousand two hundred dollars?

We don't know. We can't know, because the calculation is a lot more complicated than it appears. It depends on where the $4200 came from (capital gains? wages? interest?), whether or not you're married, how many dependents you have (and whether or not you can claim yourself as a dependent), whether the amount is gross, AGI, or taxable income, and lots of other things..