Warren paid $20 per share for 100 shares of Oil Well Mutual Fund in 2001. He received dividends of $150 per year in 2008 and 2009 that were reinvested to purchase 50 new shares of the fund. What is Warren's average cost per share for this investment?

a) $20.00 per share

b) $15.50 per share

c) $15.33 per share

d) $16.00 per share