(X,Y) has density 3x^2 + 1/2 on [0,1]x[0,1].

I need to compute the joint density of Y and Z where Z = XY.

I tried substituting X = Z/Y into the (X,Y) but that didn't work...My next guess is to just multiply X*Y together, to get the density of Z. I'm lacking a formula to put that into to find the joint distribution of Z and Y, so maybe that isn't right.

Some direction would be appreciated.