You don't need a macro. Put -1 in an empty cell somewhere (e.g. cell E1). Select the cell with the -1 in and click copy. Then click on cell C6, hold down the CTRL key and click on cell C10, then hold the CTRL key again and click on cell C12. Then right-click and choose Paste Special, and click against Values and against Multiply, then click OK and press the <Esc> key. Then you can remove the -1 from the first cell.

If you really need a macro then turn the Macro Recorder on and complete the above steps.

Hope this helps.

Pete