Based on the common recommendations, elementary-age children (typically ages 6 to 13) are usually advised to get about 9 to 12 hours of sleep per night. Since the possible responses include "about 12 hours," "about 10 hours," and "exactly 10 hours," the most appropriate answer would typically be "about 10 hours" if we assume this is the average recommendation for that age group. However, if the graph specifically states a number, it would be best to refer to that directly.
If you have access to the specific bar graph, you should select the option that matches the data shown for elementary-age children. Without that specific information, "about 10 hours" is a reasonable choice based on general sleep guidelines.