common and treasury stock
	
	
		I am learning accounts on my own,so I was trying to work on the balance sheet.I tried to answer couple of questions.I am not sure if I have the right answer.I am listing a part of the balance sheet and other stuff
Figure given is in millions:-
On the balance sheet under the stockholders equity account.I  have the following data
consolidated balance sheet:
Stockholders Equity
                                                                                                    1999           1998      
common stock ( authorized 500,000,000 shares of $2.50 par               818            818
value each;issued 1999 and 1998:327,125,854)
additional paid in capital                                                                   1321          718         
Retained Earnings                                                                            13445       12,887          
Treasury stock at cost(shares 1999:103,844,216;                             (7010)        (6647)           
 1998:106,749081)                                                                                                           
Net stockholders Equity                                                                   8323          7429
Consolidated statements of stockholders equity:
                                                                                                      1999            1998
Common Stock                                                                                
  Balance at beginning and end of year                                              $818              $818 
Treasury stock                              
Balance at the beginning of the year                                                      (6647)       (5935)   
purchases                                                                                           (429)         (742)
sales of treasury shares in the open market                                        39                  -
issuance to employees and employee plans                                         27                21
reclassifications related to put options                                                  -                  9 
balance at the end of the year                                                             (7010)       (6647)
My questions are as follows
1)how many shares of common stock is the company authorized to issue?
My ans(authorized 500,000,000) as per the balance sheet,please correct me if I am wrong
2)How many shares of common stock has the company actually issued at December 31 1999?
ans( as per the balance sheet the combined figure of 1999 and 1998 issued shares is given
as:327,125,854.So I subtracted this combined figure from the data in 1998 which is 
818000000 and that gives me:49087415,please correct me)
3)How many shares of common stock are outstanding at December 31,1999?
Ans(all I know is the formula to calculate the outstyanding shares,formula is
issued shares -outstanding shares=treasury shares.
How do we use this formula here to get an answer?
4) why do companies repurchase their own shares?
Ans)when the selling price of the share falls bellow the actuial cost of the share,secondly
when the company wants to distribute shares to its own employees.Please corect me if I am wrong
Can some expert answer these questions?
Thanks
Jeff