Shown below is information relating to the stockholders' equity of Robertson Corporation at December 31, 2017: 12% cumulative preferred stock, $150 par, 100,000 shares $1,500,000 authorized, 10,000 shares issued Common stock, $1.50 par, 1,000,000 shares authorized, 900,000 600,000 shares issued Additional paid-in capital: preferred stock 300,000 Additional paid-in capital: common stock 900,000 Treasury stock (at cost: 6,000 common shares) 180,000 Retained earnings 1,350,000 Refer to the above data. How many shares of common stock are outstanding? O a. 600,000 O b. 606,000 O c. 594,000 d. Some other number