Final answer:
Sara's thoughts on the weather and regular activities while walking to campus suggest she was experiencing happiness, as her mindset reflects contentment and satisfaction without any negative emotions.
Step-by-step explanation:
When Sara was walking to campus, thinking about the good weather, how many people were already at campus, and stopping by the bookstore, she was experiencing a state of mind that can be described as happiness. The scenarios provided in the question such as appreciating a nice day and considering routine activities like stopping by the bookstore do not typically induce stress or negative emotions but rather a sense of contentment and normalcy, which aligns with the feeling of happiness. This feeling is a positive emotion marked by pleasure, comfort, and satisfaction. As Sara's thoughts were centered around pleasant aspects of her day and not focused on worries, fears, or excessive excitement, it suggests that she was in a pleasant emotional state.