The original principal of Margaret's car loan was $15,594.29.
To find the original principal of Margaret's car loan, we can use the simple interest formula:
Interest = Principal x Rate x Time
Given that the interest is $7,638.20, the rate is 9.8%, and the time is 5 years, we can rearrange the formula to solve for the principal:
Principal = Interest / (Rate x Time)
Principal = $7,638.20 / (0.098 x 5)
Principal = $7,638.20 / 0.49
Principal = $15,594.29
Therefore, the original principal of the loan was $15,594.29.