Simple...
you have: [tex]F= \frac{G m^{2} }{ d^{2} } [/tex]
You want to find m-->>>
1.)Isolate m
[tex] d^{2} *F= \frac{G m^{2} }{ d^{2} } * d^{2} [/tex]
Leaving you with...
F*[tex] d^{2} [/tex]=[tex]G m^{2} [/tex]
Keep isolating m-->>>
[tex]F* d^{2} =G m^{2} [/tex]
[tex] \frac{F* d^{2} }{G} = \frac{G m^{2} }{G} [/tex]
Square root to solve what just m is-->>>
[tex] \sqrt{ \frac{F* d^{2} }{G} } = \sqrt{ m^{2} }[/tex]
=[tex] \sqrt{ \frac{F* d^{2} }{G} } =m[/tex]
That is how you solve for m...
Thus, your answer.