Given parameters

j=I;
(Subscript[i, pol])={2.83,45°};
(Subscript[v, pol])={100,0°};
(Subscript[r, 1])=50;
(Subscript[r, 2])=50;
(Subscript[l, 1])=25;

Convert polar to rectangular form

pol2rect[r_,θ_]:=r*Cos[θ]+j*r*Sin[θ];
(Subscript[i, s])=pol2rect[(Subscript[i, pol])[[1]],(Subscript[i, pol])[[2]]];
(Subscript[v, 2])=pol2rect[(Subscript[v, pol])[[1]],(Subscript[v, pol])[[2]]];

Circuit equations are as follows:

currenteqn1=(Subscript[i, s])+i==(Subscript[i, 1])+(Subscript[i, 2]);
volteqn1=(Subscript[v, 1])==(Subscript[r, 1])*(Subscript[i, 1]),(Subscript[v, 1])==j*(Subscript[l, 1])*(Subscript[i, 2]),(Subscript[v, 2])==i*(Subscript[r, 2]);

Solving the equations for I unknown

Solve[{currenteqn1,volteqn1},i]

(**)

ClearAll["Global`*"]

Is=2.83*(E^(I*45Degree));
Us=100*(E^(I*0Degree));
R1=50;
R2=50;
ZL=I*25;
currenteqns={Is+IR2==IR1+IZL,0==IU+IR2};
componenteqns={U1==IR1*R1,U1==IZL*ZL,U2-U1==R2*IR2,Us==-U2};
eqnsTogether=Union[currenteqns,componenteqns];
sol=Solve[eqnsTogether][[1]];
f=50;
T=(1/f);
ω=2Pi*f;
resIR1=IR1/.sol;
Plot[Im[resIR1*(E^(I*ω*t))],{t,0,3T},PlotStyle->{Thick,Green}];
Print["IR1= ",resIR1,"  A, i.e. amplitude= ",Abs[resIR1]," A, angle= ",Arg[resIR1]," rad"]

(*homework> graph of all currents denoted by names*)