Final answer:
To calculate the total interest paid, use the formula for calculating the monthly payment on a loan and subtract the principal amount from the total amount paid. In this case, Colin paid a total of $5,685.60 in interest over the life of the loan.
Step-by-step explanation:
To calculate the total interest paid, we can use the formula for calculating the monthly payment on a loan:
Monthly Payment =

Where P is the principal amount ($24,000), r is the monthly interest rate (6.5% / 12), and n is the total number of months (72).
Substituting the values into the formula and solving for the monthly payment, we get:
Monthly Payment = $402.90
Therefore, Colin would have made monthly payments of $402.90 over the life of the loan. To calculate the total interest paid, we can subtract the principal amount from the total amount paid:
Total Interest Paid = (Monthly Payment * n) - P
Substituting the values, we get:
Total Interest Paid = ($402.90 * 72) - $24,000
= $5,685.60
Colin paid a total of $5,685.60 in interest over the life of the loan.