Actually this is what I am after:

Column A (qty) Column B (unit Price) Column C (total price)

21 7 147
26 7 182
28 8 224
33 8 264
77 10 770

Colume A and B are known. Column C is variable.
Is there anyway to insert one simple same formula into all the cells in
column C. Also, how to insert one formula into all the cells in column C?
Can we avoid cell specific, such as using A1, becuase the cell name will
change after sorted and moved into both different column and row of
department master account?

Thank you for you'all