Assuming that your 401(k) has no basis in nondeductible contributions, which is usually the case, if you take out $3,400, the entire $3,400 is includible in your taxable income no matter how much of that $3,400 is withheld for taxes. The amount withheld for taxes has no effect on the income tax consequences, it only affects whether or not you might be subject to an underpayment penalty.
Whether or not 10% withholding would be sufficient to cover the additional income tax liability resulting from the distribution depends on your marginal tax rate which is not determined until you take into account all income and deductions for the the year.
