Do you want to increase every price by 20% or by 120%? Your example is
incorrect, but implies an increase of 120% If so, choose an empty cell
somewhere and put 2.2 in that cell (2.2 = 220%, which is 120% on top
of 100%). Select that cell again and click <copy>. Then move your
cursor and highlight the prices in the price column, then Edit | Paste
Special | Values (check) | Multiply (check) | OK, then <Esc>
Then you can delete the 2.2 from the original cell.
If you meant to increase the prices by 20%, then you would start with
1.2 (120%) in the first cell.
Hope this helps.
Pete