The opportunity cost of attending state college is $20,000.
The computation is given below:
= $60,000 - $50,000
= $10,000
= $40,000 + $10,000 - $30,000
= $20,000
= $15,000 + $20,000 - $20,000
= $15,000
So, the opportunity cost of attending state college is $20,000.
Learn more about the opportunity cost here: brainly.com/question/13036997