How do you solve systems of equations with 3 variables? And what if one of the equations only has 2 of the variables?
Example:
1) 2x+3y-4z=20
2) 3x-2y+z=12
3) 5x-2z=4

Don't try to solve this one, I just made it up to give you an example.

1) 2x+3y-4z=20
2) 3x-2y+z=12
3) 5x-2z=4

To solve x , y, and z : to solve this you have to reduce this to 2 variables (x and y).

As (3) 5x-2z=4 --> -2z=4-5x --> 2z=5x-4 --> z=2,5x-2
So z=2,5x-2 and therefore 4z=10x-8

Now use these solutions for z in (1) and (2) and solve x and y

1) 2x+3y-4z=20 --> 2x+3y-(10x-8)=20
2) 3x-2y+z=12 ----> 3x-2y+(2,5x-2)=12

Succes !

:)