Hi! I'm happy to help.
To solve this we need to know what is happening. This line segment was split into two parts by H. GH (part 1) and HI (part 2).
These two parts together equal the total length of the line segment. We learn that GH is 3, and HI is 12.
12+3=15
Now, we know that GI has a length of 15.
I hope this was helpful, keep learning! :D
