Kinematics: Radioactive decay and momentum

A radioactive atom at rest with a mass of 100×1027 kg100\times 10^{-27}~kgundergoes decay to three particles with masses of 25×1027 kg25\times 10^{-27}~kg , 40×1027 kg40\times 10^{-27}~kg and 35×1027 kg35\times 10^{-27}~kg respectively. Assume that all three particles remain in the x-y plane.

If the first particle is moving in the direction of positive y axis at speed of 20m/s and the second particle moves in the direction of 25 degree clockwise respect to positive x-axis at speed of 15 m/s, what is the angle and speed of the of the third particle?

(Note: if you are wondering why the masses don't add up, it's because of special relativity and mass-energy equivalence. Something to Google if you're interested. If these were anything other than atomic nuclei, though, you should expect the masses to add up properly.)
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