(-∞,4). All I did was isolated x, and it says that x has to be less than 4. That means anything before 4 is fair game. Since the problem said that it can't be equal to 4 (as it would have had to have a line under the less than symbol), I used parenthesis on the 4 side as opposed to hard brackets. The <span>∞ always requires parenthesis. </span>
