Example 1 (V and SA)

ContourPlot3D[x*y*z==1000,{x,0,40},{y,0,40},{z,0,40},AxesLabel->{x,y,z},ViewPoint->{1,1,1}]

Manipulate[Show[ContourPlot3D[x*y*z==1000,{x,0,40},{y,0,40},{z,0,40},AxesLabel->{x,y,z},ViewPoint->{1,1,1}],ContourPlot3D[2x*y+2y*z+2z*x==S,{x,0,40},{y,0,40},{z,0,40},ContourStyle->Green]],{S,0,1000}]

Example 2

ContourPlot[x^2+y^2==1,{x,-2,2},{y,-2,2}]

Manipulate[Show[ContourPlot[x^2+y^2==1,{x,-2,2},{y,-2,2}],ContourPlot[2x^3+y^4==S,{x,-2,2},{y,-2,2},ContourStyle->Red]],{S,-10,10}]

Example 3 (14.8 #15)

Show[ContourPlot3D[x+y+z==1,{x,-3,3},{y,-3,3},{z,-3,3},AxesLabel->{x,y,z},ViewPoint->{1,1,1}],ContourPlot3D[y^2+z^2==1,{x,-3,3},{y,-3,3},{z,-3,3},ContourStyle->Red]]

Manipulate[Show[ContourPlot3D[x+y+z==1,{x,-3,3},{y,-3,3},{z,-3,3},AxesLabel->{x,y,z},ViewPoint->{1,1,1}],ContourPlot3D[y^2+z^2==1,{x,-3,3},{y,-3,3},{z,-3,3},ContourStyle->Red],ContourPlot3D[x+2y==K,{x,-3,3},{y,-3,3},{z,-3,3},ContourStyle->Green]],{K,-2,3,.1}]

14.8 #20

ContourPlot[x^(1/2)+y^(1/2)==5,{x,0,25},{y,0,25}]

Manipulate[Show[ContourPlot[x^(1/2)+y^(1/2)==5,{x,0,25},{y,0,25}],ContourPlot[2x+3y==S,{x,0,25},{y,0,25},ContourStyle->Red]],{S,0,125}]