Shaving 39 minutes off my second marathon: Is it possible?

The second marathon I will run in the Sportsfest Shamrock Marathon in Virginia Beach on March 18, 2006. Last year I ran the Shamrock half marathon and it was a lot of fun. I ran the Richmond Marathon in a time of 4:24:12. To qualify for the Boston Marathon I will have to run it in under 03:15:00, so I will have to shave off about 69 minutes. That's an average of about 11.5 minutes for each of my next six marathons. However, my goal for this marathon is actually 03:45:00. This is 39 minutes faster. It may sound like an impossible time, but I like to challenge myself. Also, during my training for the Richmond Marathon, I broke my little toe, so I missed out on 4 long runs. I feel if I can stay healthy and complete all my long runs, that will significantly help me meet my goal in March. And, the weather at the Richmond Marathon was very warm. If it had been in the 50's that day, I probably would have decreased my time by 15 or 20 minutes. I began my training for the Shamrock Marathon in mid November. So far, I am injury free and sticking to my training program. I ran 18 miles on December 24th. It was a good run and I felt great.