Answer: The energy equation is [tex]E = mc^{2}[/tex], if you want the solution for mass, then you want the mass alone in one side of the equation. You can do this in the next way:
[tex]E = mc^{2} - >\frac{E}{c^{2} } = \frac{m}{c^{2} } *c^{2} = m[/tex]
where i divided by c square in both sides of the equation.
Then if you know the mass energy of an body (and the velocity of the light), with the equation [tex]m = \frac{E}{c^{2} }[/tex] you can obtain the mass of such body.
