Ohhhh okay, so I'm not supposed to switch products over reactants to reactants over products. The reciprocal is only to be done on the Kf value.
In that case, that is what I was doing wrong.
Kd = 3.57x10-16 = (x)(4x)4/(0.50-x)
x = 2.3x10-4 M
= [Zn2+]
Wow that was a rather simple problem. I feel kind of dumb for not getting it earlier, lol.
Thanks for all the assistance! I appreciate the guidance, and not just showing me the way and the answer.