Symbol for X : [tex]\tt _{31}^{64}Ga[/tex]
Radioactivity is the process of unstable isotopes to stable isotopes by decay, by emitting certain particles,
Zinc-64 undergoes beta decay, so :
The atomic number will increase by +1, and the mass number will remain the same
So that the atomic number:
30 + 1 = 31
The element with atomic number 31 is Gallium
Reaction
[tex]\tt _{30}^{64}Zn\Rightarrow _{31}^{64}Ga+~_{-1}^0\beta[/tex]