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