tolong ya kx..pertanyaannya ada di gambar...

a = 16 kursi
b =4 kursi
s15=?

sn
[tex] \frac{n}{2} (2a + (n - 1)b)[/tex]
s15
[tex] \frac{15}{2} (2 \times 16 + (14) \times 4[/tex]
[tex] \frac{15}{2} ( 32 + 56) = > \frac{15}{2} (88) = 15 \times 44 = 660 \: kursi[/tex]