I found that if the bank loan is within the term, it only takes simple interest. If overdue, the interest on overdue loans is compound interest. Due to Li's overdue repayment, it will be calculated according to simple interest. Converting the interest rate into days is 0.036%. Then use 20000+(20000*0.036%)*3. The answer on the calculator is 2002 1.6. In other words, you only need to return 2002 1.6.