For those of you with interest in the topic, but no answer yet, I just figured it out. The key was to begin the equation the way I normally do, using the "Professional" format to generate the basic fraction format. I then used the formatting dropdown attached to the equation box to shift to "Linear" mode. In that mode, I could see the general algorithm for fractions. So, I completed the work in Linear, then used the pulldown to shift back into Professional mode.