If the interest is $90 from $750 loan amount, we can calculate the periodic (4 weeks) interest rate of the loan using the below formula.
*interest amount / loan amount x 100 = periodic interest rate of loan*
To integrate the values, we have:
$90 / $750 = 0.12 multiplied to 100 will result to 12.
Therefore, the periodic interest rate of loan is 12% or $90 is 12% from loan amount of $750.