tolongin dong makaseeeyang udah jawab

a = 204
b = 4
Un = 386
n = ?
Un = a+(n-1)b
396 = 204 + (n-1) × 4
396 = 204 + 4n-4
396 - 204 + 4 = 4n
196 = 4n
49 = n

Sn = n/2(U1+Un)
= 49/2(204+396)
= 49/2×600
= 14.700