Mr. Hellerstein is a professor at Tahoe Law School located in Tahoe California. He lives in Nevada and commutes to Tahoe Law School, which is only a 50-mile, commute one way.  During academic semesters, Professor Hellerstein commutes to Tahoe, California, Monday through Thursday each workweek to teach his classes and meet with his students.  On Friday, he stays at home, where he prepares examinations, writes student recommendations and conducts scholarly research and writing.  When school is not in session, and during his sabbatical leave, he works exclusively in Nevada. On his nonresident income tax return filed in California, he apportioned to California the percentage of his total salary that reflected the number of days he commuted to the law school.  California disagrees and states that the entire law school salary is subject to California taxes. Mr. Hellerstein appeals the decision.

You are a Supreme Court judge and this case has come before you.  Please give me your decision.