Two objects x and y with a total mass od 2.5 x 10^3 kg are joined together in outer space and are at rest. An astronaut in a space shuttle presses a button that is explosive and separates the two objects from each other. X moves to the right with a velocity of 4.8 m/s and Y moving to the left with velocity of 2.5 m/s what is the mass of X?

So I know p=mv but how am i supposed to find the mass if I only know the total mass am i over looking something?

Initial momentum=final momentum

0=m4.8+(2.5E3-m)(-2.5)

solve for one mass m, then the other 2.5E3-m