Hi MathBlaster47,
There are several ways to solve a system like this, but your way seems to be a good start.
(1)
(2)
(3)
Solve (2) for z:
Substitute this for y in (1) and (3).
(1)
(3)
Solve these two equations for x and y by using substitution or elimination method. Then, substitute your value for y into (2) to find z.
(1)
(3)
Multiply (1) by 5. Multiply (2) by 3.
(1)
(3)
Add (1) + (3).
I'll leave the rest for you. Good luck.