3+6+9+12+.... Tentukan jumlah 10 suku pada deret diatas makasih

diket:a=3
r=un/un-1
=6/3
=2
s10=a(rn-1)/r-1
=3(2^10-1)/2-1
=3(20000000000-1)/1
=59.999.999.997

a= 3
b = 3

s10 = ½n (a+Un)
= ½.10 ( 3+10 )
= 5 . 13
= 65