Combining count queries into one table row
Define Query objects (call them QRented and QInventory) with SQL definitions as you have provided:

(SELECT Machine.MNAME, Count(Rental.Mid) AS CountOfMID1
FROM Machine JOIN Rental ON Machine.[MID] = Rental.[MID]
GROUP BY Machine.MNAME;)


and this:

(SELECT Machine.MName, Count(Machine.Mid) AS CountOfMID
FROM Machine
GROUP BY Machine.MName
ORDER BY Machine.MName;)


Now create a combined query from your Query objects like this:

SELECT QInventory.MName, QInventory.CountOfMID as Inventory,
    QInventory.CountOfMID  - QRented.MIDI as Available,
    QRented.MIDI  as Rented
FROM QQInventory
LEFT JOIN QRented on QQInventory.MName = QRented.MName
ORDER BY Machine.MName;