Bantu donk...........

16,19,22,25,28,31,34,37,40,43,46,49,52,55,58,61,64,67,70,73,76

a) b = 3
b) Suku tengah = 46
c) banyak suku = 21
d) S21 = 21/2(16+76)
= 966

semoga membantu
maaf kalau salah