On January 1, 2018, Edward Corporation had 12,000 shares of $4 par value common stock and 12,000 shares of 5%, $100 par value convertible preferred stock outstanding. The preferred shares carried a 3-for-1 conversion privilege. On October 1, 2018, all of the preferred shares were converted to common. What number of shares must Edward use in computing basic earnings per share at December 31, 2018?

• 9,000.

• 21,000.

• 48,000.

• 12,000.