In $2002$ Mary purchased $10$ shares of Acorn Corporation common stock for $$100.$ In $2005$ Mary purchased an additional $10$ shares of Acorn Corporation common stock for $$200.$ At the end of $2007,$ Acorn Corporation declared a $2$ for $1$ common stock split. What is Mary's total basis in her Acorn Corporation common stock? a$)$$$600$; b$)$$$400$; c$)$$$500$; d$)$$$300$