Tradewind Aviation, which provides round trip flights from Teterboro airport in NJ to Martha's Vineyard and Nantucket, in Mass., recently hired a new accountant. The accountant's first task was to determine the number of Tradewind's outstanding shares of its common stock. In reviewing Tradewinds General Ledger, the accountant determined the following: Common stock, par $10 (authorized 25,000 shares). However, the balance in the Common Stock account was $200,000 Treasury Stock (at cost $15 per share). However, the balance in the Treasury Stock account was $900.

Based on the above data, how many of Tradewind's shares of common stock are outstanding.