Question

Like a good economist, you calculated the opportunity cost of getting your college degree. suppose that at your university, you will pay $12000 each year for tuition, $3000 each year for textbooks, and $12000 per year for room and board. before you left for college, your boss at your high-school job offered you a job paying $15000 per year. assume that if you decided not to go to college, your parents would not let you live at home. what is your opportunity cost for four years of college?

Answer 1

Opportunity cost of going to college is actually the salary forgone. 
With a yearly salary of $15,000 and a rent of $12000 yearly (parents would not let you live at home), we are left with $15000 - $12000 = $3000 per year 
For 4 years, the opportunity cost will be 4 x $3000 = $12000

Answer 2

The opportunity cost of going to college should include the direct costs of getting an education (tuition and books) plus the income you could have earned if you did not go to college. Over four years, the opportunity cost is equal to:

4 × ($15000  + $2500 + $20000) = $150000