1. The problem is to express the equation $E=mc^2$ in terms of $m$. 2. The formula given is Einstein's mass-energy equivalence formula: $$E=mc^2$$ where $E$ is energy, $m$ is mass, and $c$ is the speed of light. 3. To express $E$ in terms of $m$, we note that $c$ is a constant (speed of light), so the equation is already solved for $E$ in terms of $m$. 4. Therefore, the expression for $E$ in terms of $m$ is simply: $$E=mc^2$$ 5. This means energy $E$ is equal to mass $m$ multiplied by the square of the speed of light $c^2$. Final answer: $$E=mc^2$$