I'm starting with the formula m=(s-c)/s but I know what m and c are so I need to figure out what s is. But I have no idea how to do that. I've tried using real numbers eg. 0.17=(264-219)/264 but I just can't figure out how to get the number 264 when starting with 0.17 and 219... This is really doing my head in, I wish I'd paid more attention at school... Can any help explain how to get s on the left side of the equation?