Momentum & Collision question?

A 8.4 kg puck floating on an air table is traveling east at 16 cm/s. Coming the other way at 26 cm/s is a 2.3 kg puck on which is affixed a wad of bubblegum. The two slam head-on into each other and stick together. The velocity after impact is 6.97 cm/s. How much kinetic energy (in J) is lost?