Bagi yang bisa dijawab ya. Mksh

Un = ar^(n-1)
U2 = ar = 10
U5 = ar^4 = 10/27
(ar)r^3 = 10/27
(10).r^3 = 10/27
r^3 = (10/27) / 10
r^3 = 1/27
r^3 = (1/3)^3
r = 1/3
ar = 10
a.1/3 = 10
a = 3.10 = 30
Sn = a ( 1-r^n ) / ( 1-r )
= 30 { 1 - (1/3)^n } / ( 1- 1/3)
= 30 { 1 - (1/3)^n } / 2/3
= 45 { 1 - (1/3)^n }

di ket : u2 = 10
: u5 = 10/27
un = a x r^5 - 2 = a x r^3
10/27 = 10/x r^3
r^3 = 10/27 : 10
r^3 = 10/27 x 1/10 = 10/270
r = 3√1/27
r = 1/3
dit jumlah n 1
u2 = 10
un = a x r^n-1
10=a x 1/3
a = 10 : 1/3
a = 30
jadi jawabanya yang C