Calculation method of interest:

Can be obtained according to the interest calculation formula.

Formula: principal * interest rate * years = interest.

For example, the principal is 100000 and the interest rate is 7.8%.

Then 15 interest =100000 * 7.8% *15 = 7800.

The monthly repayment of principal and interest is157800/72 = 2191.67 yuan.