If x, y, z are all variables to be found, then there are an infinite number of solutions, because we would need 3 equations for a unique solution.
The second equation can be divided by 2: 2x+4y=z, or 2x=z-4y.
The first equation can be written: 2x=5z-3y, therefore 5z-3y=z-4y, y=-4z.
So 2x=z+16z, x=17z/2.
Now we have x and y in terms of z, and that’s as far as it goes. We can choose any value of z and find values for x and y. That gives us many solutions.