....... ... ............

U2=19
U5=31
eliminasi
U2= a+ b =19
U5= a+ 4b=31
-3b=- 12
b= -12/-3
b= 4
a+b=19
a+4=19
a= 19-4
a=15

U50=a+49b
= 15+49(4)
= 15+196
= 211
S30= 30/2 (2(15)+29(4))
= 15 (30+116)
= 15(146)
= 2190