b)
[tex]x=-4, \ y=-3, \ z=-12\\\\\frac{12xy}{x^2}=\frac{12\cdot(-4)\cdot(-3)}{(-12)^2}=\frac{12\cdot12}{(-12)\cdot(-12)}=\frac{144}{144}=\boxed1[/tex]
c)
[tex]d=3, \ e=-2\\\\6de-3e^2+4d^2=6\cdot3\cdot(-2)-3\cdot(-2)^2+4\cdot3^2=\\\\=-36-3\cdot4+4\cdot9=-36-12+36=\boxed{-12}[/tex]
d)
[tex]m=\frac{1}{4}, \ n=2\\\\\frac{m}{n-4}=\frac{\frac{1}{4}}{2-4}=\frac{\frac{1}{4}}{-2}=\frac{1}{4}\cdot(-\frac{1}{2})=\boxed{-\frac{1}{8}}[/tex]
