Your answer is in the question; that is, if you have transcribed the question correctly.

##PbI_2(s) rightleftharpoons Pb^(2+) + 2I^-##

You have been quoted the concentration of plumbic ions, ##Pb^(2+)##. It is easy to see why this concentration is equal to the required solubility. As a followup to this question, what do you think the examiner means by "saturated solution"?

pur-new-sol