Jawabanmu

2014-09-09T20:16:43+07:00
* a+(n-1)b=19
  a+(2-1)b=19
  a+1b = 19
*  a+4b= 31

# a+1b=19 - a+4b=31
 -3b= -12
b= -12/3
=-4
# a+1b=19 ⇒ a+1.-4=19
a+(-4)=19
a= 19+4
= 23