; or (2) an amount equal to the sum of the outstanding balances (equal to the sum of the unpaid principal, interest, penalties, and fees) that the borrower owes on such loans. (c) Methods of repayment A borrower who expects to have an annual repayment amount for the taxable year that is greater than the amount specified in subsection (f)(1)(D) shall make payments through the following methods: (1) With respect to any wages earned by the borrower that are subject to Federal income tax withholding, the withholding process described in section 499E(a)(10). (2) The monthly payments process described in section 499E(c), to meet the portion of the borrower’s obligation that is not paid through withholding, or, in the case of a borrower who opts out of the withholding process, to meet the borrower’s entire obligation. (3) The direct payments process under section 499E(a)(4). (4) The process described in section 499E(a)(5) that allows other individuals or entities to make payments on the borrower’s annual repayment amount for the year. (d) Order of crediting Payments on loans made under this part shall be applied, without regard to the method of such payments, first toward penalties due on the loans, next toward any fees due on the loans, then toward any interest due on the loans, and finally toward the principal due on the loan with the highest applicable rate of interest among such loans. (e) Prepayment authorized A borrower shall have the right to prepay all or part of such loan, at any time and without penalty. Any such prepayment amount will be applied to loans made under this part in the same order as described in subsection (d). (f) Underpayments (1) Penalties for underpayments (A) In general Subject to subparagraph (C), if, as of the last day of a taxable year, a borrower has not paid at least 90 percent of the borrower’s annual repayment amount for such year, the borrower shall be charged a penalty in an amount equal to 10 percent of the difference between— (i) an amount equal to 90 percent of the borrower’s