A rifle is test fired into a ballistic pendulum. The bullet embeds itself in the block of mass 0.55kg that makes up the bob of the pendulum. The pendulum hangs by a massless string of length 0.85 kg. When hit with the bullet the pendulum swings up in an arc of 65 degrees from the vertical before falling back. The recovered bullet has a mass of 3.5 g. What is the muzzle velocity of the rifle?