You’re trying to reach a whole by having the fraction 26/26
You can add 12/26 + 8/26 = 20/26
Then take 26/26 - 20/26 = 6/26
note: if the question wants you to simplify you would divide both your numerator and your denominator by 2 to get 3/13 as your final simplified answer.
21.4 i did it already for s1
in which figure is point g a centroid