Forms :: Search And Compare Value From Three Tables In A Form

I have three tables: Table A, Table B and Table C

Fields of Table A: Truck No, Capacity
Fields of Table B: Consignee ID, Capacity A, Capacity B and
Capacity C
Fields of Table C: Consignee ID, Final Rate

Input form is based on Table C:

1-I select Truck No using a combo box and it shows the Capacity from Table A using DLookup.
2- I enter the id no. in the field of Consignee ID and it returns the values of Capacity A, Capacity B and Capacity C using DLookup from Table B.

So I have to write manually one final rate in the field of Final Rate in the form.So I want:When I enter id no. in the field of Consignee ID, it matches with the Capacity in Table A and shows the matched result only in the field of Final Rate of Table C.