Ok, assuming both tables have the positions spelled identically I would do it this way:
1. Create a query (assuming the table name is 'AVAILABLE' for available positions)
Code:
SELECT [Pay Rate], Position, Count([Position]) as PositionsAvailable FROM Available GROUP BY Position, [Pay Rate]
This query should give you a list of positions and a count of available positions
2. Create a query (assuming the table name is 'FILLED' for filled positions)
Code:
SELECT [Pay Rate], Position, Count([Position]) as PositionsFilled FROM Filled GROUP BY Position, [Pay Rate]
this query should give you a list of positions and a count of filled positions
3. Link the two queries together through the position field, make sure the queries are linked FROM the available query TO the filled query, add the positionsavailable field and the positionsfilled field, then do your % filled calcuation using [positionsfilled]/[positionsavailable]