Next May, I am running my first Marathon. I have ran 3 half marathons, with my most recent this May when I ran 1:27. I ran this off 30 mile weeks. I am setting a goal of 3:15 for my first Marathon. How much do I need to increase my mileage to reach my goal or should I aim for a faster time? I am a 27 year old male. Any training advice would be appreciated.