bagaimana 2 soal ini menyelesaikan ini?

jawab

ax + y + 2z = 5
bx -y + 3z = 3  ||(+)
(a+b)x  + 5z = 8
7x + 5z = 8 ..(i)

ax + y + 2z = 5
cx -y + z = -1 ||(+)
(a+c)x + 3z = 4
5x + 3z = 5 ..(ii)

(i) dan (ii)
7x  + 5z = 8 } kali 3
5x +  3z = 5 } kali 5

21x + 15z = 24
25x + 15z = 25 || (-)
-4x = -1
x = 1/4

5x + 3z = 5
5(1/4) + 3z = 5
5/4 + 3z = 5
3z  = 5 -5/4 = 15/4
z = 15/(4)(3) = 5/4

nilai 12x +8z = 12(1/4) + 8(5/4) = 3+ 10
12x + 8z = 13