Tack the plywood to the top of the ledger, making sure it's tight. Place the joist hanger around the 2x4 and nail 16d galvanized nails through all the holes into the ledger board. Cut the 2x4 to ...

Pull out and replace rusted or corroded nails. Joist hangers used outdoors are usually attached with galvanized joist hanger nails, but you can also use screws if recommended by the manufacturer.