From what I can see, you are on the right track.
one thing you could have done is combine like terms.
[tex] {10}^{2} - {3}^{2} = {7}^{2} [/tex]
Now just take the square root of 7 squared. That takes out the squared making your answer 7 or G.
You were on the right track, you just skipped a step.
hope this helped!