Tolong jawab beserta jalannya

13. U2: 13 U12: 73
a. beda
u12= 73
u2= 13
_______ _
10b= 60
b= 6

b. S36?
cari a dulu--> u2=a+(n-1)b
13=a+6
7=a
s36=n/2 (2a+(n-1)b)
=36/2 (2.7+35.6)
=18(14+210)
=4032

14. a. suku pertama= -8
beda=3
b. s30?
s30= n/2(2a+(n-1)b)
=30/2(2.-8+29.3)
=15(-16+87)
=1065