Hello! Lets solve this step by step! :)
Okay so we are ganna use the Pythagorean theorem.
Since we know that FG = 10 cm, BC = 8 cm, and AB = 9 cm, we can now plug those numbers into our equation. So we take 8 squared + 9 squared = c squared
So thats 81+64=c^2 145=c^2
and √145 =12.0415945788
Now we round it to the nearest tenth of a centimeter and that gives us 12.04 So thats our answer! :)
Hope this helped if you have any other questions or would like further explanation just let me know!! :)