The amount you will repay can be solved by:
Amount to be repaid = ( $ 1, 431 borrowed) ( $ 0.31 per day / $ 500 borrowed) 151 days
Amount to be repaid = $ 133.97
The annual interest rate is:
1431 + 133.97 = 1431( 1 + i)^ 151(1/360)
Solve for i
i = 0.2378 or 23.78 % per year