The formula for determining simple interest is expressed as
I = PRT/100
where
P = principal or initial amount borrowed
R = interest rate
T = time in years
I = interest
If $100000 was borrowed and $129750 was repaid, it means that the interest is
I = 129750 - 100000 = 29750
T = 4 years
P = 100000
Thus, we have
29750 = (100000 * R * 4)/100
29750 = 4000R
R = 29750/4000
R = 7.44
The interest rate is 7.44%
