The formula for the gravitational force between two objects is $F=\frac{G{m}_1{m}_2}{r^2}$, where $F$ is the force, $G$ is the gravitational constant, $m_1$ and $m_2$ are the masses, and $r$ is the distance between their centers. Which equation correctly expresses $r^2$ in terms of $F$, $G$, $m_1$, and $m_2$?