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To the right we have the graphical solution when the RHS = 10.   The optimal solution to this problem is x = 5, y = 5 which has an objective value of 6 2/3.

Now lets look at what happens if we further decrease the right hand side of the second constraint from 10 to 5.

 

To the right we have re-graphed the constraint.   Again, the dotted line represents its old location, while the solid line is its new one.   We have again moved this constraint out and added the darker green area to our feasible region.

With this new feasible region, is our old solution (the blue dot) still optimal?

 

As before, we can push our objective function from the dotted blue line, to the solid blue line.   This gives us a new optimal solution with a new objective value.