Uggh... I am doing the same thing right now, and not fully understanding either, but I'll try to explain.
What I was told is to solve the first equation for x or another variable. In this case, it would be easier to do z because it doesn't have a number next to it. Basically, get all of the other junk on the other side so it is "z = blah blah blah."
Then, do the substitution method. If you don't know how to do this, write a response back and I'll explain more in depth. But basically, in the second and third equations, substitute z for whatever you got on the other side of the equal sign (should be -5x - 2y - 25).
That makes there only be x and y in the second and third equations. Then, if you know how, do elimination. If you don't know how to do this, either, I can explain more in depth if you respond back.
After that, solve one of the variables in the equation, and then find the other.
You should have an ordered triple instead of the ordered pair. Instead of the usual answer (x,y) it should be (x,y,z), or three answers, one for each variable.
Hopefully I helped!
now I'm confused even more