.
If you need the formulas, then you may learn them from your textbook (which I insistently recommend).
If you need the numbers only, you may use some of numerous online calculators for loans.
For example, this one https://www.calculator.net/loan-calculator.html
which is free of charge.
It gives for the 1st scenario Total of 36 Payments $6,969.71
for the 2nd scenario Total of 48 Payments $7,584.14
The difference $7,584.14 - $6,969.71 = $614.43 is your ANSWER.
It is the amount Samantha can save.
Solved.