Question

Three bullets are fired simultaneously by three guns aimed toward the center of a circle where the bullets mash into a stationary lump. The angle between the guns is 120°. Two of the bullets have a mass of 9.30 10-3 kg and are fired with a speed of 440 m/s. The third bullet is fired with a speed of 650 m/s and we wish to determine the mass of this bullet.

Answer 1

Unless you tell us something about the velocity of the resulting 3-bullet lump, there's no way to tell anything about its mass.

Also, are the three gun muzzles arranged in a circle parallel to the plane of the target?