Answer:
I believe your answer is 9 if the length of H to F is 10.
Step-by-step explanation:
This is because if you plug 9 into the question mark and add 1 ( Which is the length of G to F), then the length of H to F would be equal to the blue line.
HG + GF =HF
HG= 9
GF= 1
HF= 10
9+1=10
