Bob,
A couple of things. You wrote that you used the following: St+(ha-Med(ha))*4 . I see two possible places where you may have messed up. First, "St" should be written as "$T" which means the target you are applying the formula to. Second, you need to take out the term "ha" in both instances and replace it with the name of your own Ha image. Easiest way to do that is to open the expression editor in PixelMath, highlight "ha" and then select the appropriate image (which you need to have open) from the images log. Double click on that image name and it will replace "ha". Then simply apply the formula to your Red image.
Hope that helps,
Jim