Contour Graph does not include Boundary Values

[Keyur-Gondaliya]

Here when we set step size So boundary values should be added in it's first respective close container.
Ex lower bound value should be in first range and upper bound value should be in last range

When we set step size should be 2 and min=2 and max=8, here expected result should be
2<=x<=4
4<x<=6
6<x<=8