Answer:
1.)
2.) 13
Explanation:
For the first question you just need to see where the missing segment starts and ends. Then you could write it either way EF or FE. I prefer to keep it in order from left to right.
Now for the second question you just have to take the value of the segment that's known and subtract it from the whole segment value to find the missing segment. So in this case we would do 34 - 21 and that will give us 13, so the missing segment is 13.