x + y = 14 y + z = 18 x + z = 20 Maka x + y + z = ?

x+y = 14
y+z = 18
----------- -
x - z = -4

eliminasi dengan pers ketiga
x+z = 20
x-z = -4
------------ -
2z = 24
z = 12

subtitusi ke pers 3
x + 12 = 20
x = 20-12
x = 8

subtitusi ke pers 2
y + 12 = 18
y = 18-12
y = 6

maka
x+y+z = 8+6+12 = 26