In[]:=
Z[x_,y_]=x+2y+8
Out[]=
8+x+2y
In[]:=
Show[ParametricPlot3D[{x,0,
2
x
},{x,-5,5}],Plot3D[Z[x,y],{x,-5,5},{y,-5,5},AxesLabelAutomatic,Lighting"Neutral"],BoxRatios->{1,1,1}]
Out[]=