Final answer:
The independent variable in this study is the amount of time Hailey spends studying.
Step-by-step explanation:
The independent variable in this study is the amount of time Hailey spends studying. This is because Hailey wants to determine if the time she spends studying affects her grades. The independent variable is the factor that is being manipulated or changed by the researcher, in this case, the amount of time spent studying.