When there is no express written contract fixing a different rate of interest, interest shall be allowed at the rate of ten per cent a year, except that, with respect to obligations of the State, interest shall be allowed at the prime rate for each calendar quarter but in no event shall exceed ten per cent a year, as follows:
(1) For money due on any bond, bill, promissory note, or other instrument of writing, or for money lent, after it becomes due;
(2) For money due on the settlement of accounts, from the day on which the balance is ascertained;
(3) For money received to the use of another, from the date of a demand made; and
(4) For money upon an open account, after sixty days from the date of the last item or transaction.
As used in this section, "prime rate" means the prime rate as posted in the Wall Street Journal on the first business day of the month preceding the calendar quarter.