tolong di jwb ya kaka kaka hansome and beautiful:-)

n=4 , a=25 , U4=200
U4=a.r³
200=25r³
r³=200/25
r³=8
r=2
Sn=a(rⁿ-1)/(r-1)
Sn=25(2⁴-1)/2-1
Sn=25(16-1)/1
Sn=25(15)
Sn=375cm