When the boundary line is dashed it means that it is greater than or less than. When the boundary line is solid it means that it is greater than or equal to or less than or equal to.
Boundary lines are dotted whenever the sign is strictly greater than or less than.
The only reason a line is not dashed would be that it would be equal to. A quick way to remember this would be that the extra line provided to make it equal would fill in the blanks. Hope this tip helps you, helped me ace many tests!
