This is an arithmetic progression since the difference (d) between 2 consecutive terms is constant:
13=5 = 8
21-13 = 8
29-21 = 8, etc.
If a is the first number (5) & d=8 & n=100 Then value of the term X with nth rank ===>X(nth) = a+(n-1)d ===> 5+(100-1).8 = 797 (I can't read the second question, the photo is too dark
