Substitution Method: Substitute the value of one variable in other two to get 2 - variable system
Example:
x + y + z = 6
2x - y + z = 3
x + 2y - z = 2
Put x=6-y-z from the first equation into the last two equations to get 2 variables, 2 equations system and solve it to get y and z. Then, compute x.
