Barisan Geometri. U3= 12, dan U6=96. S4. . . ?

U6 = 96 = rumus  ar^n-1
u3 = 12
s4 ?

u6 = ar^5  u3 = ar^2
96 = ar^5  12 = ar^2

r = 6-3√96/12 = ∛8 = 2
S4 = u3 x r
     = 12 x 2 = 24
S4 = 3 + 6 + 12 + 24 = 45