As of June 30, 2012, Superior Company has Current Assets with a book value of $600,000 and a market value of $550,000. The Long-term Assets have a book value of $980,000 and market value of $850,000. Its Current Liabilities have a book and market value of $300,000 and the Long-term Liabilities have book value of $700,000 with market value of $600,000. What is the difference between the book value and market value of its Stockholders' Equity?
a. $180,000
b. $500,000
c. $80,000
d. $130,000