Removing the 4 13 mm bolts on the rear brake drums

Removing the 4 13 mm bolts on the rear brake drums I am doing the rear brakes on my 05 focus. I found the 4 bolts that hold the hub on and don't ya know that when i went to remove them I had one snap off. I used some spray but these are rusted and very tight. What is the best way to remove the other 7 bolts without breaking them off like i did the first one.