The very first step is writing out the balanced equation.  This way you will see the mole ratio of each component in the overall equation.  Next, you have to take a look at the masses of the reactants given to you.  Based upon the balanced equation you have written, which reactant is going to be completely consumed?  (I.E. what chemical will be all used up and what one will be in excess?)  Once you have that figured out, you can easily set up a ratio, using the balanced equation, to see how many moles of zinc sulfate you'll wind up with.  Once you've figured out the number of moles, finding out the mass is simple.  

All salts exists in solution as mixture of ions. The lowest solubility shows K2SO4. Hence you will not isolate desired ZnSO4 from solution.

But that does not matter in this case.  The question is simply designed to help teach limiting factors in reactions.  Therefore, whether they are soluble or not does not matter one iota.  

If that is the case, then it is a bad question or the OP was not sufficiently clear with hist question. Initially, I could not do anything with this question, I simply did not understand it, because no reaction occurs if these two compounds are mixed. There are much better examples of (really occurring) reactions, where one of the reactants is the limiting compound in the total reaction result.

I agree wholeheartedly with Wilco. There are enough examples of real reactions to be used in such cases to not justify using fake ones. This is a bad habit displayed by some stupid teachers - all it does is it adds confusion. Even without bad examples chemistry is full of overgeneralizations that make it hard to understand once you learn that what you have learnt before is only half-truth.