Monggo jawabin mas/mbak pusing nih

jawab
n = 5
a= 16
u5 = 81

u5 = a r^4 = 81
16. r^4 = 81
r^4 = 81/16 = (3/2)^4
r = 3/2

sn = a. (r^n - 1) / (r - 1)
s5 = 16 . (3/2^5  -1) / (3/2  -1)
s5 = 16 (243/32  - 1) / (1/2)
s5 = 32 (243/32 - 1)
s5 = 243 - 32 = 211