ACTON, Mass. - Shareholders of Co-operative Bank of Concord and Bank  of Braintree have approved the acquisition of Braintree by Walden Bancorp,   a new holding company formed by Co-operative for the merger.   
Under the deal, shareholders of both banks will receive one share of  Walden stock for each of their shares in a tax-free transaction. The new   company will have about $1 billion in total assets, with $785 million in   deposits and $91 million in equity.     
  
The deal is expected to close Friday, pending state regulatory  approval. 
Co-operative also announced that it had sold its Medford office to  Century Bank and Trust Co., with $20 million in deposits, resulting in an   after-tax gain of $575,000.   
  
Co-operative has $765 million in assets, with 16 branches in three  counties. Braintree has $217 million in assets, with three branches in   Norfolk County.