Tolong dibantu dong no 13 & 14

a = suku pertama = 10°
beda= 10°
Un = a + (n-1) b
200 = 10 + (n-1) 10
200 = 10 + 10n - 10
n = 20

Sn= n/2 (2a + (n-1)b)
Sn= 20/2 (20 + (19)10)
Sn= 10 (20 + 190)
Sn= 10×210
Sn= 2100
Sn= 11 2/3 π (π=180°)