7,11,15,19,...103 tentukan jumlah bilangan?please bantu donk

u1 = 7
b = 4
Un = 103
U1 + (n-1)b = 103
7 + (n-1)4 = 103
7 + 4n -4 = 103
4n + 3 = 103
4n = 100
n = 25

Sn = n/2(U1 + Un)
= 25/2(7 + 103)
= 25/2(110)
= 25 x 55
= 1.375

maaf gak pake cara
jawabannya 5355