Jawabanmu

2014-08-16T14:43:35+07:00
A + 7b = 15 ........... (1)
a+b + a +15b = 26 jadi 2a+16b = 26 ..... (2)
eliminasikan pers 1 dan 2
 b=-2 , a= 29

U20 = a+19b = 29 - 38 = -11