Tolong dijawab ya kakak

a+4b=29
a+10b+59  lalu eliminasi
6b=30
b=5
a=9

S40= 20(18+5(39))
= 20 (18+195)
=20 (213)
=4260

U5 = 29
U11 = 59

pertama, cari b

(59-29)/(11-5)
=30/6
=5

Un = a+(n-1)b
U5 = a+(5-1)5
29 = a+20
a = 29-20
a = 9

Sn = n/2 (2a+(n-1)b)
S40 = 40/2 (2(9)+(40-1)5)
S40 = 20 (18 + 195)
S40 = 20 (213)
S40 = 4260