bantu bantu master. matematika matematika hadehhh

diketahui :
a = 12
b = 4
Un = 48

Un = a + (n - 1) b
48 = 12 + (n - 1) 4
48 = 12 + 4n - 4
4n = 48 - 12 + 4
4n = 40
n = 40/4
n = 10

Sn = ...?
Sn = 1/2 n (a + Un)
S10 = 1/2 x 10 (a + U12)
S10 = 5 (12 + 48)
S10 = 5 (60)
S10 = 300