*Is* it dissociated in a 1:1 ratio?

Right, I understand it is dissociated in a 1:2 Zn:CN ratio, but i still can't figure out the answer.

By this logic it must follow that (assuming the concentrations of Zn and Cn are x) : x^3 = Ksp = 2.56 × 10^-13.

Taking the cube root does not give me an answer of 8.0 × 10^-5.

Back-tracking, cubing 8.0 × 10^-5 gives me a value of 5.12×10^-13, which is twice the Ksp value. There's something not quite right here