A Uranium Nucleus (Mass 238 Units)at Rest Decays into a Helium

A uranium nucleus (mass 238 units) at rest decays into a helium nucleus (mass 4.0 units) and a thorium nucleus (mass 234 units) .If the speed of the helium nucleus is 6.5 × 10⁵ m/s,what is the speed of the thorium nucleus?

A) 1.1 × 10⁴ m/s
B) 3,802.5 × 10⁴ m/s
C) 1,440.0 × 10⁴ m/s
D) 2.1 × 10⁴ m/s
E) ​0.1 × 10⁴ m/s