Let G be a finite group. The aim of this paper is to study the number of solutions \(S\subseteq G\) of the equation \(\mho ^{\{n\}}(S)=L\) , where L is a non-empty subset of G, n is a positive integer and \(\mho ^{\{n\}}(S)=\{ s^n \ | \ s\in S\}\) . Besides our findings obtained in this general frame, we also outline some results which hold for some particular cases such as: (i) L is a normal subset of G; (ii) G is abelian; (iii) G is an extraspecial p-group.