F.N.B. Corp. and OBA Financial Services Inc. announced Thursday that OBA shareholders have approved OBA’s acquisition by F.N.B. OBA, the parent company of OBA Bank, has six branches in Montgomery, Anne Arundel and Howard counties. As announced on April 8 and as approved by the boards of directors of both companies, shareholders of OBA will be entitled to 1.781 shares of F.N.B. common stock for each common share of OBA. The all-stock transaction is valued at approximately $23.56 per share, or about $94 million. The deal is expected to close on Sept. 19, the companies said. F.N.B., a financial services company headquartered in Pittsburgh, is the parent firm of First National Bank of Pennsylvania and Regency Finance Co. Last year, F.N.B. acquired Baltimore County Savings Bank for $79 million.