text: Use the conservation of momentum.  Calculate the momentum of puck A and momentum of puck B after the collision.  Do a vector addition of this momentum to get the total momentum of puck A before the collision.  This will give you the velocity of puck A before the collision allowing you to calculate the kinetic energy before the collision.  You also have the velocity and masses to calculate the kinetic energy after the collision.\n\nEquations:\nmomentum  is mass * velocity\nenergy is mass * velocity ^ 2 / 2