Consider the results of a survey where students were asked about their GPA and also to break

Question:

Consider the results of a survey where students were asked about their GPA and also to break down their typical 24-hour day into study, leisure (including work), and sleep. Consider the model GPA = β0 + β1Study + β2Leisure + β3Sleep + .
a. What is wrong with this model?
b. Suggest a simple way to reformulate the model.