Divide top and bottom by 3: (2b-1)/((b-2)(b+2). Excluded values: b=-2 and 2. The variable b can take any other values in the set of real numbers. As b gets larger, the expression approaches 2b/b^2=2/b, so the expression gets closer and closer to zero from a negative and positive direction, and where b is between -2 and 2. The range of the expression is all real numbers.