The radius of a nucleus of mass number 64 is 4.8 fermi. Then the mass number of another nucleus having radius of 4 fermi is $\frac { 1000 } { x }$, where $x$ is $\_\_\_\_$.
The radius of a nucleus of mass number 64 is 4.8 fermi. Then the mass number of another nucleus having radius of 4 fermi is $\frac { 1000 } { x }$, where $x$ is $\_\_\_\_$.