Write SQL query to solve given problem: How many businesses are registered in the database under 'Banks & Credit Unions' category?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T2.business_id) FROM Categories AS T1 INNER JOIN Business_Categories AS T2 ON T1.category_id = T2.category_id WHERE T1.category_name = 'Banks & Credit Unions'