I- interest rate refers to the ratio of interest to principal;

I- interest;

F- the sum of principal and interest, also known as the sum or final value of principal and interest;

N-the number of interest periods.

interest

=

capital

*

interest rate

*

Number of interest-bearing periods

I

=

P

*

I

*

n

∫ The score is 10 times that of Li, so the annual interest rate is 5 points, which means the annual interest rate is 50%; A monthly interest rate of 5 points means a monthly interest rate of 5%.

∴ The annual interest rate is 1.5 and 15%.

interest

=

Thirty thousand

*

15%

*

four

=

18000 yuan

Answer: interest 18000 yuan.