need help with calculation:

you owe $2154.35 on your PBnJ credit card that has an interest rate of 9.85% APR, rather than placing $435 into a savings account earning 2.5% APR, you pay down the principal at the beginning of the month on the credit card. How much interest did you save? (HINT: Calculate the difference between the interest you would earn from the savings account and the interest you would pay on your credit card for the $435)​