A Student Has a Job That Pays a Wage Rate

Multiple Choice

A student has a job that pays a wage rate of $10 per hour. The night before an economics exam, the student has set aside four hours to study for the exam, estimating that for each hour spent studying, her grade will rise by 5 points. That night, she gets a call from her employer to come to work for a wage rate of $15 per hour for that night. She decides to work for three hours and earn an extra $45.00. The next day she takes the test and gets a grade of 75. The opportunity cost for her work is

A) the $45.00 she earned.
B) the 15 extra points she estimates that she could have earned on the exam if she had studied the extra three hours.
C) the three hours she did not study.
D) the entire four hours she set aside for studying.