Two pieces of clay collide and stick together moving in one dimension. Clay 1 has a mass of 2,100 grams, and clay 2 has a mass of 2,500 grams. Clay 1 has an initial velocity of 20 m/s and clay 2 has an initial velocity of -10 m/s immediately before they have a perfectly inelastic collision. What is the final velocity of the two pieces of clay immediately after the collision?