The annual interest rate is 6.31% plus 79 (meaning an increase of 0.79%), the annual interest rate is 7.1%

The one-time repayment interest at maturity = principal × annual interest rate of the loan × Loan time = 3 million × 7.1% × 1 = 213,000 yuan

The interest for equal principal and interest repayment is 11.66 yuan

The interest for equal principal repayment is 11.54 yuan