Code:

polys = Graphics3D[{Opacity[0.2],
LightPurple, {Polygon[{{5, 0, 5},
{-5, 0, 5}, {-5, 0, -5},
{5, 0, -5}}]}}];
polys2 = Graphics3D[{Opacity[0.8],
LightPurple, {Polygon[{{5, 5, 0},
{-5, 5, 0}, {-5, -5, 0},
{5, -5, 0}}]}}];
c1 = ContourPlot3D[{2*y^2 == x}, {x, 0, 5},
{y, -2, 2}, {z, 0, 5}]
p1 = Plot3D[4*(1 - x/4 - y/2), {x, 0, 4},
{y, 0, 2}, PlotStyle -> {Opacity[0.5]}]
p2 = Plot3D[4*(1 - x/4 - y/2), {x, 0, 4},
{y, 0, 2}, PlotStyle -> Blue,
RegionFunction -> Function[{x, y},
x > 2*y^2 && 4*(1 - x/4 - y/2) > 0]]
final = Show[{p1, p2, polys, polys2, c1},
BoxRatios -> {1, 1, 1}, AxesLabel ->
{Style["X", 20], Style["Y", 20],
Style["Z", 20]}]
domain = Plot[{Sqrt[x/2], 2 - x/2},
{x, 0, 5}]
GraphicsGrid[{{domain, final}}]