First, we need to find the interest. This is given by
which gives
a) What is the amount of the final payment?
The final payment is given by
Then, the answer is $619.9758
b) How much does he save by paying the loan off early?
Since the loan is for 12 months, the total payment is
Therefore, the amount saved is given by
which gives
Therefore, the answer is $6.4242 saved