z varies directly with y and inversely with w and x2. When y=12, w=2, and x= - 2, z= - 18. What is the equation of variation?

z =( k y ) / (w* x) we need to solve for k.....the constant of proportionality

So we have

-18 = k (12) / (2 * -2)

-18 = k (-3) divide both sides by -3

6 = k

So, the equation is

z = (6y) / (w*x)