= (150,000*12/12) + (10,000*10/12) + (16,000*5/12) - (12,000*2/12

why we did multiple by 12,10,5 and why we divided by 12

could you explain the answer in detail ?

Earnings per Share Stanford Corporation began the year with 150,000 shares of common stock outstanding. On March 1 an additional 10,000 shares of common stock were issued. On August 1, another 16,000 shares of common stock were issued. On November 1, 12,000 shares of common stock were acquired as Treasury Stock. Stanford Corporation's net income for the calendar year is $489,000. Required Calculate the company's earnings per share. Earnings per Share $ 3