[tex]2y+5x-z=4y+6x\ \ \ \ \ \ |subtract\ 4y\ from\ both\ sides\\\\-2y+5x-z=6x\ \ \ \ \ |subtract\ 5x\ from\ both\ sides\\\\-2y-z=x\ \ \ \ \ \ |add\ z\ to\ both\ sides\\\\-2y=x+z\ \ \ \ \ \ |divide\ both\ sides\ by\ (-2)\\\\\boxed{y=-\frac{x+z}{2}}\\\\==============================\\\\8xy=z\ \ \ \ \ \ |divide\ both\ sides\ by\ 8x\\\\\boxed{y=\frac{z}{8x}}[/tex]