A loan of $39,000 is paid off in 36 payments at the end of each month in the following way: Payments of $975 are made at the end of the month for the first 12 months. Payments of $975 + x are made at the end of the month for the second 12 months. Payments of $975 + 2x are made at the end of the month for the last 12 months. What should x be if the nominal monthly rate is 12.8%