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Others say this is on the old study design but I'll take a crack anyway. $3000 deposit means we have already paid $3000. Therefore we must pay $12000 off the loan.
36 monthly payments = 12 payments per year over 3 years
If we pay $400 monthly, that is $4800 per year. If we are paying off a $12000 loan over three years that can equate to paying $4000 off the principal each year.
Therefore, if we pay $4800 each year, but only paying off $4000 off the principle, we are paying $800 interest. 800/4000 = 0.2. Therefore, the annual interest rate is 20%.
E.
Not a great explanation, let me know if I am incorrect
Hope that helps!