Okay. The first thing to remember is that the molar solubility = Ksp. The only difference between molar solubility and normal solubility is that molar solubility REQUIRES the value to be given in moles per liter. Normal solubility can be given in any mass/volume unit. (So if they say that something has a solubility of .04 g/L, it's molar solubility would be (.04/molar mass)/L).

You can tell that (1) and (2) are the same based upon the units. Number 1 states that the concentration of your zinc hydroxide in solution is 2.7x10^{-6} mol/L, and number 2 is giving the solubility in terms of moles/L. Therefore in this instance the molar solubility and solubility given are the same.

For your hypothetical equation, every mole of A3B4 that dissolves gives 3 moles of A and 4 moles of B. So your Ksp equation would be:

Ksp = [A^{+4} ]^{3} [B^{-3} ]^{4}. Your 'I.C.E.' chart would look like the following:

.[A^{+4} ].[B^{-3} ]

Initial: 0 0

Change: +x +1.3333x

Eq: x 1.3333x

If x is calculated to be 1 mole/liter, your concentrations would be 1 mole/liter for the A ion, and 1.3333 moles for the B ion. The solubility of the initial compound would then be 1/3rd the concentration of A, or 1/4 the concentration of B. So in the end, the result would be 0.333 mole/L.