mohon bantuannya ya, terima kasih. : )

Sn = 1/2n (a + Un)
S5 = 1/2.(5).(125.000+65.000)
= 5/2. 190.000
= 475.000 (jawabannya C)

b = (65.000 - 110.000) / 3
= - 15.000

a = 110.000 - (-15.000)
= 125.000

U2 = a + b = 110000
U5 = a + 4b = 65000
b = (U2 - U5)/(2 - 5)
b = (110000 - 65000) / (-3)
b = 45000/(-3)
b = -15000

a = U2 - b = 110000 - (-15000) = 125000

Total uang = S5
S5 = n/2 (a + U5)
S5 = 5/2 (125000 + 65000)
S5 = 5 × 95000
S5 = 475000