Thanks Pierre and Tim:
I see now how the ({x}==5?0.8:0) works. When x=5 the expression 5==5 is true and returns 5*4-0.8=19.2, otherwise it returns {x}*4, which within the range of 3-6 yields 12, 16, 19.2, and 24.
When I posted originally, I had tried to put calculations in the question but didnt' realize that the {=(expression)} syntax was necessary. Thanks for pointing that out.