1. Suppose the annual interest rate is r (indicating the proportion of interest to be paid every year).

2. the total interest I can be calculated by formula I = p× r× n.

3. Where P= principal (i.e. loan amount), r= annual interest rate (expressed in decimal form, such as 5% annual interest rate as 0.05) and n= loan period.

4. according to the topic P=45000, n=3 years.

5, in order to simplify the calculation, assume that r=0.05 (that is, the annual interest rate is 5%).

6. I can be obtained by substituting the known value into the formula.

7. It can be concluded that the interest on a 3-year loan of 45,000 yuan is 6,750 yuan.