Half cell reactions are
at anode: Cu⇋Cu2++2e−
at cathode: CuS+2e−⇋Cu+S2−
so, overall cell reaction is: CuS⇋Cu2++S2−
now, as Eocell=(Eoreduction)C−(Eoreduction)A
=EoCuS|Cu−EoCu2+|Cu
=x−0.34 V
Cell is in equilibrium, therefore, Ecell=0
So, Ecell=Eocell−0.0592log[Cu2+][S2−]
0=(x−0.34)−0.0592log[Cu2+][S2−]
Eocell=0.0592logKsp
=0.03 log(8×10−36)
=0.03[3log 2−36]
=0.03[3×0.3−36]
=0.03(−35.1)=−1.05 V
=x−0.34=−1.05 V
=−0.71 V
hence, EoCuS|Cu=−0.71 V