No 16 serta pembahasan nyaa

Cara cepat

U3 - U8 = 2 - (-13)
2b - 7b = 15
-5b = 15
b = 15/-5
b = -3

Cari nilai a

U3 = a + 2b
2 = a + 2(-3)
2 + 6 = a
8 = a


Cari U15 :
U15 = a + 14b
U15 = 8 + 14(-3)
U15 = 8 - 42
U15 = -34

MAKA
S15 = 15/2 (a + U15)
S15 = 15/2 (8 - 34)
S15 = 15/2 (-26)
S15 = -195

Jawaban E