How to get the specific repayment interest when repaying USN?

(1) When all USN is repaid, all interest shall be repaid;
(2)When only part of USN is repaid, the corresponding proportion of interest shall be repaid;
(3) If there are multiple records to be repaid, the default is to repay one by one from the earliest generated record, and the repayment interest is also added one by one.