A closed circle on a number line indicates that the endpoint is included in the solution set. This corresponds to inequalities that are "greater than or equal to" (≥) or "less than or equal to" (≤). Among the options provided:
- \( x \geq 3 \) includes the value 3 itself, which means that it will have a closed circle at 3.
The other inequalities ( \( x > 0.4 \), \( x > -3 \), and \( x < 4 \) ) would have open circles since they do not include the endpoint.
Therefore, the inequality that has a closed circle when graphed on a number line is: \( x \geq 3 \).