RegionPlot3D[
z >= ((x)^2 + (y)^2) &&
z <= 3 Sqrt[x^2 + y^2],
{x, -3, 3}, {y, -3, 3}, {z, 0, 9},
AxesLabel -> {x, y, z},
Mesh -> True,
PlotRange -> {{-3, 3}, {-3, 3}, {0,9}},
PlotPoints -> 500]
RegionPlot3D[
z >= ((x)^2 + (y)^2) &&
z <= 3 Sqrt[x^2 + y^2],
{x, -3, 3}, {y, -3, 3}, {z, 0, 9},
AxesLabel -> {x, y, z},
Mesh -> True,
PlotRange -> {{-3, 3}, {-3, 3}, {0,9}},
PlotPoints -> 500]