For all such problems, start with this:

Varying           "directly" or product of "jointlys" or 1 if none 
quantity  = k * ----------------------------------------------------------
                inversely variable or product of "inverselys" or 1 if none

In this problem the varying quantity is x.
there are no "directly"s or "inverselys", so we have
the product of the jointlys on top and 1 on the bottom:





>>...x = 2 when y = 3 and z = -4...<<

Substitute these values and solve for k:











Next substitute -1/6 for k in





That is the complete equation of variation,
which can be used to find any one of the three
variables when two of them are given

>>...find y when x=8 and z=1 <<

Now we substitute those values into



and solve for y.

I'll let you do that.  If you have trouble, you
can tell me in the thank-you note form below,
and I'll get back to you by email.  No charge, 
as I do this for fun.  :)

Edwin