请大家帮我看看这道题

A corporation with 5000000 shares of publicly listed stock reported total earnings of $7.20 per share for the first 9 months of the operation. During the final quarter the number of publicly listed shares was increased to 10000000 shares, and fourth quareter eranings were reported as $1.25 per share. What are the average annual eraning s per share based on the number of shares at the end of the year?

A.     1.83

B.      2.43

C.     4.85

D.     8.45

E.      9.70

正确答案是C，但我没什么思路是怎么算得。请大家帮帮忙。