Any person (except an employee who acts without knowledge) who knowingly violates the rules of this subpart shall be liable to the United States for a civil penalty as stated in part 386, appendix B, of this chapter, and if any such violation is a continuing one, each day of violation will constitute a separate offense. The amount of any such penalty shall be assessed by FMCSA's Administrator, by written notice. In determining the amount of such penalty, the Administrator, or his/her authorized delegate shall take into account the nature, circumstances, extent, the gravity of the violation committed and, with respect to the person found to have committed such violation, the degree of culpability, any history of prior violations, ability to pay, and any effect on ability to continue to do business, and such other matters as justice may require.