What is the sum of the first five terms of the series 35 30 25

By keenly investigating the given sequence, it is evident that is an arithmetic sequence with a common difference (d) of -5. To solve for the sum (S) (also called arithmetic series), 
                                  Sn = (n/2) x (2a1 + (n - 1) x d)
where n is 5 and a1 is 35. Substituting the given known values, 
                                  S5 = (5/2) x (2 x 35 + (5 -1) x -5) = 125
Thus, the sum of the first five terms is 125. 

Why are u not just putting the numbers this is to much

Answer d; a supplementary angle = 180°, so if that angle = 150°, y would = 30°.