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Here is a possible way to do it fo the first two planes. It should be straightforward to add the third.

var('u,v,w')
plane_1=implicit_plot3d(2*u+  v+  w== 5,(u,-10,10),(v,-10,10),(w,-10,10),opacity=0.7,color='red')
plane_2=implicit_plot3d(4*u-6*v    ==-2,(u,-10,10),(v,-10,10),(w,-10,10),opacity=0.7,color='blue')

plane_1+plane_2

You may try this code over at sagecell.