Tolong Bantu saya nomor 2 please besok kumpul

barisan aritmatika : 20, 24, 28, , U25, maka
suku pertama a = 20, beda b = 4, n = 25
Un = a + (n -1).b
U25 = 20 + (25-1).4
= 20 + 24.4
= 20 + 96
= 116
b) S25 = n (U1+U25)/2
= 25/2 (20+116)
= 25/2 (136)
= 25.68
= 1.700 kursi