Don't give up on us yet!!!! You said the values in C could be anything but at the start, you seemed to imply it would be either 12 or 15, what is the spreadsheet for?
Its a FTSE 100 spreadsheet and the results are either a "WIN" or a "LOSS" depending on this outcome effects the value in the next cell ei if its a "WIN" the value need to be 12 if it's a "LOSS" the value needs to be 15.
TCL is quite correct, the basic if function I supplied will return a false value no mater whats in the cell if it's not "win" his is a far better method.