Given your answer is say x<3, "x is less than 3", that means that 3 is not included in your solution set. The interval (-∞, 3); note the use of parenthesis. If the interval is [-3,6), this means that in your solution 3 is included but not 6. That is to say, 3≤x<6. [3,6]; both are included. (3,6) none is included.