Three guns are aimed at the center of a circle, and each fires a bullet simultaneously. The directions in which they fire are 120° apart. Two of the bullets have the same mass of 3.86 x 10-3 kg and the same speed of 330 m/s. The other bullet has an unknown mass and a speed of 601 m/s. The bullets collide at the center and mash into a stationary lump. What is the unknown mass?