NMaximize[{X1,{-1≤X2≤1,-1≤(X1/4-X2/2)≤1,-1≤(X1/2-X2/2)≤1}},{X1,X2}]

Solve[X1/4-X2/2==1,X2]

Solve[X1/2-X2/2==1,X2]

g1=1/2 *(-4+X1)

g2=1

g3=-2+X1

g4=-1

Plot[{g1,g2,g3,g4},{X1,-3.0,6.5},PlotRange->{{-3.0,6.5},{-3.0,3.0}},Filling->Bottom]
Show[%, Frame->True,GridLines->Automatic,FrameLabel->{X1,X2},LabelStyle->Directive[Red]]