Tolong kerjain, pake caranya ya dan jelaskan caranya?

Un = a + (n - 1)b
U6 = a + (6 - 1)b = a + 5b = 18
U10 = a + (10 - 1)b = a + 9b = 30
________________________–
-4b = -12
b = 3

a + 5b = 18
a + 5(3) = 18
a + 15 = 18
a = 3

Sn = n/2 × (2a + (n - 1)b)
S16 = 16/2 × (2(3) + (16 - 1)3)
= 8 × (6 + (15)3)
= 8 × (6 + 45)
= 8 × 51
= 408

silahkan lihat gambar di atas
maaf kalau salah semoga membantu :)