Excel how to add (+) from one sheet to appear in another?

Im trying to add e.g £1.99 from one sheet (CELL) to £65 thats on another Sheet. iv tried so many different functions using =sum but its not what im looking for. I dont want to have to put =SUM(C:C)+SOLD!$C3 in the £65 cell as there is already a function in there (=sum(C:C)) So is there a function i can use in the £1.99 Cell for it to be added onto the £65 Cell.

Iv explained as best i can.
These are the formulas that i have tried so far:
='C'!F2+0.5
=C5+1.99 * 'C'!F2

I think i want something like that but the result keeps ending up in the £1.99 cell and not the £65 one.

Hi, thanks for the reply, this one is working but its doing the opposite:

Sub MACRO3()

     Range("C5").Value = Range("C5").Value + Sheets("C").Range("F2").Value

End Sub

The result is ending up in the opposite cell that i want it to go in. The result is going into the 'C5' Cell when i want it to go into the 'SheetC' 'Cell F2'

It may be helpful to understand this: a formula determines the value for the cell in which it is entered. It can't determine the value for other cells. At best, it can be a parameter used in the formula for your target cell.