Suppose that y varies jointly with w and x and inversely with z and y = 32- when w = 6, x = 20, and z = 3. write the equation that models the relationship

Y directly proportional to WX  and inversely to Z. 

Y=k(WX)/Z
Where k is the constant of proportionality. 
So, the first thing is to find the value of this constant. 

k = YZ/WX
  = (32×3)/(6×20)
  = 96/120
  = 0.8
The equation that models the relationship will be;
Y = 0.8(WX/Z)