tolong mas berikan jawabannya secara cepat. ni lagi tray out

jawab

u2 = 8
u4 = 14

u4 - u2 = 14 - 8
(4-2)b = 6
2b = 6
b = 3

u2 = 8
a + b =8
a = 8-3 
a= 5

Un = 23
a + (n-1)b = 23
5 + (n-1)3 = 23
3(n-1) = 18
n-1 = 6
n = 7
s7  = 7/2 (a + u7)
s7 = 7/2 (5 + 23)
s7 = 7/2 (28)
 s7 = 98

un = 23