The total of principal and interest is
... $4285 +513.26 = $4798.26
Dividing this into 36 equal payments gives a payment amount of ...
... $4798.26/36 = $133.285
There is no formula that will give the interest rate as a function of payment, principal, and time, but the appropriate equation can be solved graphically or iteratively. The result is the interest rate for this payment value is about 7.497%.
These numbers are consistent with answer choice ...
... c. 7%; 133.29
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Of course, that answer can be selected simply on the basis of the payment value.
The interest rate corresponding to a payment of 133.29 is 7.4999264%, which still rounds down to 7%.
