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.
The more trials you do, the closer the empirical probability should get to the theoretical probability. It won't be a perfect match but it will likely be close enough so to speak. Note how 70/420 = 1/6.
Idk how im supposed to answer this or whatevs bu yes i have done factoring with variables. distrubutive is the most involved in factoring method as i can tell. i dont think ive studied this before or i mightve forgoten but im sure a polynomial can be factored into another one. and yea. hope this helped in sum way