I have a spreadsheet with a worksheet that I would like to check row by row
to see if the value in Column A (1,i) and Column B (2,i) have the sames
values for other rows.

If the values in Column A and Column B match then if Column C (i,3) is blank
and the matching Column C is not blank then insert the value for the other
Column C.

Please help me complete this task.

Thanks,

Example

Column A Column B Column C
123 648 Calif
345 456 Ariz
123 648

Desired Output
Column A Column B Column C
123 648 Calif
345 456 Ariz
123 648 Calif