Answer: lowers the federal funds rate.
Step-by-step explanation:
The federal funds rate is the rate at which banks lend money to their selves overnight to ensure that they meet lending and reserve requirements.
The interest rate paid on excess reserves rate is the amount of interest that the Fed pays banks to keep excess reserves. If this rate was to decrease, banks would have less incentive to keep excess reserves at the Fed and so would have more money to meet lending and reserve requirements such that they won't need to borrow from other banks as much which would then lead to the federal funds rate decreasing due to less demand.