Final answer:
The answer is b. 4.5 years.
Step-by-step explanation:
To find the length of Madeline's loan, we can use the formula for the monthly payment of a loan:
Monthly Payment = (Loan Amount * Monthly Interest Rate) / (1 - (1 + Monthly Interest Rate)^(-Number of Months))
Plugging in the given values, we have:
$500 = (20000 * 0.071) / (1 - (1 + 0.071)^(-Number of Months))
By solving this equation, we find that the length of Madeline's loan is approximately 4.5 years. So, the answer is b. 4.5 years.