Newton's law of gravitation is $\displaystyle{F}=\frac{{{G}{M}{m}}}{{{{r}}^{{2}}}}\usepackage{cmbright}\Huge\$ , where $\displaystyle{F}\usepackage{cmbright}\Huge\$ is the force between two objects, $\displaystyle{M}\usepackage{cmbright}\Huge\$ and $\displaystyle{m}\usepackage{cmbright}\Huge\$ are the masses of the two objects, $\displaystyle{G}\usepackage{cmbright}\Huge\$ is the universal gravitational constant, and $\displaystyle{r}\usepackage{cmbright}\Huge\$ is the distance between the two objects.

By knowing information about the size of the earth and making a few measurements, this formula can allow you to determine the mass of the earth. Solve this equation for $\displaystyle{M}\usepackage{cmbright}\Huge\$ .