Using Cramer's rule, solve

2x-y=4

3x+y-z=10

y+z=3

I have no idea how to show my working on the board, but having gone through the working to the best of my ability I came up with the answer:

x=2.33 y=1.55 and z=0.11

I'm certain that I'm wrong, I checked using a math program, but I can't tell where I went wrong with my working.

Could I get a little help figuring out how to post my working, and then troubleshoot it?