tolong bantuanya. please

U1 = a = 2.
U4 = 54
ar^3 = 54
2.r^3 = 54
r^3 = 27
r^3 = 3^3
r = 3
Un = 4.374
ar^n-1 = 4.374
2r^n-1 = 4.374
r^n-1 = 2.187
(3)^n-1 = (3)^7
n - 1 = 7
n = 7 + 1
n = 8
Jadi 4.374 adalah suku kedelapan.